How is young-earth creationism theologically harmful, according to those who do not adhere to it?

I'd like to present an answer which makes no reference to modern science nor to how it appears to skeptics, but only on how we read the Bible. My thinking here is based primarily on St. Augustine's The Literal Interpretation of Genesis, which I highly recommend you look at if you're interested in the Creation debate.

I think the hermeneutical problems with YEC are twofold:

1. YEC misses the point of reading the Bible. Recall 2 Tim. 3:16-17: "All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the servant of God may be thoroughly equipped for every good work." Similarly, Paul also says in 1 Corinthians 10:11 that stories in the OT were written "for our instruction". We read the Bible not just to learn some facts, but because it's useful for Christian life. When YECs read Genesis 1-2, they look for some details about the creation of the world which have no conceivable relevance to Christian life or theology. They read Genesis 1 and think that, if they learn that God created the world over the course of 144 hours, they have understood the text. In doing this, they read the Bible as a history textbook instead of as the inspired Word of God.

2. YEC does not promote a careful reading of the Biblical text. Augustine came to the conclusion that that the six days are not literal 24-hour periods based on reading the text carefully (he was not favorable to allegorical reading of the Bible, and frequently stresses literalism and authorial intent as essential principals for Biblical interpretation). In The Literal Meaning of Genesis he spends over a hundred pages on the creation week, looking at every detail. I'll just highlight three facts that he mentions which the YECs find it difficult to account for: Firstly, what is meant by a "day" before the creation of ground, sky, sun, or moon. The Newtonian notion of some absolute, reference-independent timescale which we could measure out 24-hours against is not supported by modern science, nor was it held by Augustine and other ancient philosophers. For Augustine and modern science, time only exists as measured by the things in it. Secondly, the seventh day is given with a morning but no evening, which is hard to account for if this is meant as a normal 24-hour day. The significance of the detail is hinted at, though never explicitly mentioned, in Hebrews 3-4, where the day of God's rest is compared with our eternal rest. Thirdly, the entire Creation period is called a "day" in Genesis 2:4, so if we're insisting on reading "day" literally every time, we have immediately a contradiction.

Preamble:

When I speak of a non-YEC I speak of a person who believes God used the evolutionary process to create instead of His direct 'miraculous' agency (like speaking things into existence and going on His knees and taking dirt in His hands and forming a man, etc.) We could argue about an exact definition that includes everyone's ten cents but this one is just so you can better understand why I answer the way I do.

Answer:

Non-YECs and YEC's differ in what they believe before they read and interpret Scripture. Therefore, all theology of YECs must be viewed as detrimental to non-YECs and vice versa.

The one believes man's limited discovery and understanding of God's natural laws first, then interprets Scripture in light of this more important belief already held. The other doesn't and believes a literal reading and interpretation of Genesis.

Because the non-YEC believes that the laws we see governing the universe today have done so to bring about everything in the univers, a foundational theological detriment about YECs would have to include the belief about God Himself. How does God interact with the laws of the universe that He created when He creates and what does this tell us about Him?

If He created reality to always function just as predictable as we can clearly observe today, then it would seem dishonest to maintain a YEC interpretation. Here we have the second theological detriment - honesty.

Honesty not only of the YECs but of God Himself. If God created the laws of the universe, why then break those rules in the act of creating by the miraculous intervention that a literal reading of Genesis implies? It would seem to make no sense for a divine being that claims omniscience to make laws to govern reality if He is going to need to break them in the act of extending that reality.

It is either the natural laws of God that created or God Himself. It cannot be both for the non-YEC because the non-YEC is not making the rules of evolution - atheistic science is.

If the non-YEC chooses to believe God used evolution to create then he/she cannot depart from how atheistic science defines the 'rules' of evolution (how the universe works according to finite, atheistic, non-omniscient beings that the Bible elsewhere says are born in the darkness of sin and ignorance of God). (This is a serious theological detriment that could be discussed if the OP was framed the other way).

With an evolutionary understanding wholly dependent on man's supposed knowledge of the universe, it would seem that a YEC interpretation would make God dishonest and even struggling to create because of natural laws He made. These laws appear to modern man to be doing everything that He had to 'manually override' in Genesis 1 and 2 if we read it literally as YECs do.

These laws would seem deficient or unnecessary. If God overides them anyway in the act of creating, why have them? It paints a picture of a God that is still struggling to figure out what exactly good and necessary laws are so He can walk away and let things be; a God in need of debugging the software that runs the universe.

By extension, such a picture of God would cause serious theological concerns when we learn that He has a moral law that governs morality in His universe. It would make one question if this law needs some manual overrides when necessary?

With just dishonesty and a lack of logic as theological detriments in mind, it is easy to see why all theology of YECs must be considered detrimental in the eyes of a non-YEC.

I hope it is clear to the discerning reader that non-YECs have even greater theological detriments to answer for because of their beliefs about 'science' and that I would argue for that, but, it is beyond the requested answer scope of this question.

I would like to challenge the basis of the question rather than outright answer it. Specifically, the claim that

if such arguments can be sustained, they would be a powerful argument in favor of YEC.

This seems to me to be saying that the stricter belief is the safer belief, and the safer belief is the better belief—because it’s safer, not because it’s true.

The logic runs like so:

1. There are two opposed positions, A and B.
2. A and B are irreconcilable. (A implies not-B. B implies not-A.)
3. A asserts that the difference is, in some sense, important. (If A, then believe-B implies consequence C, and believe-A implies not-C.)
4. B asserts that the difference is not important. (If B, then believe-A does not imply C, and believe-B does not imply C.)
5. Consequence C is undesirable.
6. Therefore it is objectively best to believe A, as that avoids consequence C regardless of A or B.

It’s Pascal’s Wager all over again.

I say that this is not a good reason to hold a belief. For one thing, it produces insincere belief. If you support a position because of an argument like this, do you really believe it? Do you think it’s true, or just a safe bet?

For another thing, it is contrary to Romans 14. If the above logic were sound, wouldn’t Paul have told us all to be A-ists? But instead, he teaches that A-ists must not judge B-ists, and B-ists must not have contempt for A-ists.

So whatever you believe about these things keep between yourself and God. Blessed is the one who does not condemn himself by what he approves.

Lastly, just for the avoidance of any doubt, let me emphasise that I am not identifying Young Earth Creationism with A, and its rejection with B. I am talking about a particular line of logic that takes “I can tolerate your belief, but you can’t tolerate mine” as an argument in favour of the stricter (less tolerant) belief. Such logic can certainly be used on both sides of this, and probably any, debate.

A belief in YEC, requires believing that physical observation and scientific discovery of the universe are lies that contradict the Biblical truth.

Most logical and reasonable people will accept the reality of an ancient universe, so they must reject whatever YEC supporters are saying, which includes the validity of the biblical record. YEC is basically saying: we believe something that appears to be demonstrably false and easily disprovable, but if you are willing to believe it too, then here is what Christianity is all about … .

Fortunately, some denominations believe in a "gap theory", in which the universe was created billions of years ago (Genesis 1:1), and then rebuilt into its current form about 6000 years ago (Genesis 1:2–…). This belief fits far better into the current scientific view of the world than does the young-Earth belief.

YEC presents a system that most people simply can't accept as true, and as a result they won't even get around to looking at the essential beliefs of Christianity itself.

Although the pastoral concern would be paramount for me, since you want a theological problem with YEC, I would offer the following.

We are commanded throughout the Scriptures to seek after wisdom. That command actually has moral/theological force; it's not simply a case of “some kids are smart, and good for them.” Everyone is supposed to seek after wisdom, which of course includes consulting with people who are more intelligent or experienced than us about various matters. It's not optional.

So within that framework, there's a moral dimension to what we believe and accept, even in matters that one wouldn't initially think were matters of faith. If I go around claiming that 2+2=5, then I'm working against wisdom. Now, maybe that bit of foolishness ends with me, or maybe it means a rocket I designed crashes, or maybe it makes my kids think Christianity and mathematics are incompatible and abandon mathematics or Christianity. But whatever the outcome, it's still a sin.

I certainly grant that the scientific issues surrounding YEC are harder to sift through than 2+2. But you've got Christians going back almost to the beginning reading Genesis 1 non-literally (Origen), and you've got plenty of faithful biblical scholars and scientists in the present day, from many Christian denominations, saying that there is no conflict between the Bible and a 13-14 billion year-old universe. In that context, presenting YEC as not just one logical possibility (which I accept, given the proper qualifications), but the only correct possibility, and indeed as a crucially important doctrine, is wrong-headed to the point of exposing oneself to the charge of embracing foolishness outright.

(I want to be clear here that I can't draw a red line on many issues, to say that beyond this point, having a wrong belief is sinful. But as I'm not the Judge, that doesn't bother me.)

There are no theological problems with someone being a believer in Young Earth Creation.

If someone chooses to believe that the Genesis account is literal, then they are not sinning. Many people believed the Genesis account was literal, and there is no indication it affected their walk with Jesus. I know many people who do so today, and live virtuous lives. It is inconceivable that Jesus would look at someone who believed and trusted in him, obeyed his commands and loved God and his neighbour, but would reject that person because they had a wrong opinion about the age of the universe.

The problems all arise with YEC Christians who insist that all other Christians must believe in YEC like they do.

It is this that turns people off Christianity, and causes people to believe that Christians are delusional, and that it is necessary to reject reality in order believe in Jesus. It is this that causes people to walk away from Jesus when they discover that the simple theology they were taught is contradicted by overwhelming evidence.

Another possible downside is that some Christians insist on arguing about the age of the Earth. Non-Christians see this question as something that has very little relevance to their lives, and Christians' focus on it also puts them off the faith.

GratefulDisciple gives a good and coherent account of the damage that such insistance can do, and Ray Butterworth makes good and valid points. I won't repeat them in this answer.

YEC is theologically harmful if people reject Christ just because they don't believe certain tenets of YEC such as the six 24-hour day of creation and the historicity of Adam.

A corollary is when people reject Christ because fundamentalist Biblical inerrantist pastors / leaders convinced them that Christian faith requires reading all of the Bible as historical facts, in addition to putting our faith in Christ. A famous story back in May 2020 can serve as an example: Jon Steingard, an evangelist-pastor kid, abandoned the faith he was raised with and announced it in a series of Instagram posts. A few weeks later, he was interviewed in the Unbelievable? program with Sean McDowell (son of apologist Josh McDowell) as another guest.

A part of his decision seems to have something to do with his relying too much on the Bible being inerrant so that he always has a reliable answer for every question in life, although after watching the video it seems more to do with the hiddenness of God and with his inability to understand why the Father in Heaven would abandon helpless kids to die before they reach 5 in impoverished and dangerous places (which is so hard for him who is a father to young kids himself).

Some quotes from the Instagram post:

I was raised to believe that the Bible was the perfect Word of God. Sure, it was written by human beings, but those people were divinely inspired - and we can consider the words they wrote to be the Word of God.

I began to have questions and doubts about that. It seemed like there were a lot of contradictions in the Bible that didn't make sense. ... Suffice it to say that when I began to believe that the Bible was simply a book written by people as flawed and imperfect as I am - that was when my belief in God truly began to unravel.

...

Once I found that I didn't believe the Bible was the perfect Word of God - it didn't take long to realize that I was no longer sure he was there at all. That thought terrified me. It sent me into a tailspin. The implications of that idea were absolutely massive.

From the video (min 39:02-39:49):

"... I just came away with this feeling [that] everyone is just deciding for themselves what they want to believe. And there is no way to know for sure. That was the conclusion I reached. ... A real key point for me was the inerrancy of the Bible. ... If the Bible is not the perfect Word of God like I was taught, then to your point Sean about the anchor, what is the anchor? ..."

Sean responded with 2 points:

1. Knowledge doesn't require certainty, Christians live with doubt and are given mercy citing Jude 1:22, doubt is not the opposite of faith/belief/knowledge, what's important is what makes the most sense even when we have some doubts/questions. (min. 40:07-41:10)
2. He also believes that the Bible is "the inerrant perfect word of God", but more important to him is what is the heart central issue? He said that to Christianity it is not inerrancy. Even if we had an errant / flawed Bible (which Sean does not believe) but still show that Jesus claimed to be God, died, buried, and rose in the 3rd day, Christianity is still true. (min 41:10-42:37)

Does Paul's Christ Require a Historical Adam?

J.R. Daniel Kirk, a Fuller's NT professor, wrote a 2013 journal article "Thinking Science and Christian Faith Together" which is posted in the Fuller Seminary's blog as Does Paul's Christ Require a Historical Adam?

His main point is that for people who are convinced that the human origin story is best told from a non-YEC perspective, they don't have to abandon the Christian faith. He believes that

The task of reimagining a Christian story of origins for our modern era has already begun. ⁹

⁹ After Adam: Reading Genesis in an Age of Evolutionary Science by Daniel C. Harlow, an article in the September 2010 issue of Perspectives on Science and Christian Faith.

From His concluding paragraph:

To accompany Paul on the task of telling the story of the beginning in light of Christ, while parting ways with his first-century understanding of science and history, is not to abandon the Christian faith in favor of science. ...

Christ, the Law, and History

He assess the following question:

To what extent do we need to affirm a historical Adam in order also to affirm the saving dynamics of Paul’s Adam Christology?

and interpret Rom 5:12-21 to represent Paul's attempt 1) to take all other options other than Christ "off the table" and 2) to establish that God's people are not demarcated by Torah (i.e. Gentiles and Jews have the same problem and need Christ as the solution). He concluded this section (emphasis mine):

Paul’s Adam theology is an avenue toward affirming that God has one worldwide people; therefore, the specially blessed people are not defined by the story of circumcision. But he does not ask the question of whether an evolutionary account of human origins might stand within the story of God’s new creation work in Christ, and his argument is not aimed at denying such an explanation of where we came from.

Retelling the Story of Origins

In the second section of the article he reminded us of the perspective used by ancient writers when telling stories of human origins (such as Genesis 1), that

it was never simply to tell people “what happened.” Instead, such narratives indicate why their particular people and their particular god played the roles of sovereigns of the world.

Similarly, (emphasis mine)

Paul employs the story of Adam based on his new understanding that Christ is the man through whom God has chosen to rule the world and that the churches are the people who are the fulfillment of the promise of numerous descendants. For neither Paul nor the writer of Genesis does the story of Adam exist as a standalone narrative to which later history must correspond. Instead, the convictions about what God has done at a later point in history determine how the Adam story is read.

...

... what is a “given” for Paul is the saving event of Jesus’ death and resurrection. The other things he says, especially about sin, the Law, and eschatology, are reinterpretations that grow from the fundamental reality of the Christ event. ... The gospel need not be compromised if we find ourselves having to part ways with Paul’s assumption that there is a historical Adam, because we share Paul’s fundamental conviction that the crucified messiah is the resurrected Lord over all.

... For many, the cognitive dissonance between the sciences and a historical Adam has already become too great to continue holding both.⁸ We therefore have to carefully determine whether the cause of Christ, and of truth, is better served by indicating that a choice must be made between the two, or by retelling the narrative about the origins of humanity as we now understand it in light of the death and resurrection of Christ.

⁸ Recent Genetic Science and Christian Theology on Human Origins: An "Aesthetic Supralapsarianism" by John R. Schneider, an article in the September 2010 issue of Perspectives on Science and Christian Faith.

CONCLUSION

YEC in itself is not harmful at all. Millions of Christians have been nourished in their faith assisted by YEC-formulated theology, especially before 1800. The harm lies when a YEC church, coupled with a particular version of the inerrancy doctrine, teaches their followers in such a way (through sermons, Sunday school programs, reading list, apologetics) that resulted in

1. their misplacing the central issue of what needs to be believed away from Christ alone, by requiring them to package Christ together with reading the Bible in a certain way (such as reading Gen 1-3 as history) as though they rise and fall together
2. "protecting" them from asking the truly hard questions (problem of evil, etc.) by giving substandard apologetics based on an increasingly-hard-to-defend version of inerrancy (which is stricter than Chicago Statement), refusing to be aware that the inerrancy doctrine itself is not as clear cut as the doctrine of the Trinity. For example, see the 2020 article Inerrancy and Evangelicals: The Challenge for a New Generation.

Thus, the harm lies when YEC Christians (or would-be Christians evangelized by YEC) have doubt about Christianity. This is the time when they need to dig deep into the resources that help Christianity "makes sense" to them so they don't have unnecessary cognitive dissonance that interferes with their personal relationship with Christ. Humans are metaphysically wired to love the truth, making cognitive dissonance unbearable.

Unlike Trinity, doctrines / teachings that are still open (such as eschatology, historical Adam, atonement, nature of baptism, original sin, inerrancy) should be presented in such a way so that when a Christian has doubt he/she can switch to another theory of human origins / atonement / etc. to resolve the doubt. I myself, for example, prefer St. Irenaeus's understanding of Adam and the associated atonement theory which in doing so alleviates my personal concerns of God's justice and love, but I do not exclude the legitimacy of other Christians who prefer other theories as long as we all subscribe to the early creeds (like the Apostle's creed).

Therefore, if a YEC-promoted way of reading the Bible prevents a Christian from choosing a legitimate option of particular doctrines or from reconciling with other sources of truth (such as evolution) which could have contributed to the resolution of that doubt, then that unnecessary narrowing of theologically legitimate options is where YEC is theologically harmful.