Does every sin affect other people?

This is an interesting question especially in the case of that island. In the Biblical verse which pronounces "love one another as you love yourself", it clearly indicates that you love yourself too and hence Christ who lives in you. Every act of sin that you do have a negative impact to you or to secondary being or both. Every sin is regretted being done. SO even if it a private sin, you harm yourself and hence the Christ in you. You should see yourself and others as carriers of the Spirit of God and in every way respect and love yourself and all that exists on the face of the earth. Every sin creates an air of negativity which in turn affects everybody in that zone. Every small act leads to the courage to do bigger acts which would finally affect all people and beings around oneself, be it an act of positivism or an act of negativity

Every sin is a rebellion against God - it is the refusal to obey God's laws. So, of course, a rebellion against the Creator of the universe is going to be an action against him. So, in fact, every sin does affect people - three people, actually: Father, Son, and Holy Spirit.

As for what evil is, without 'good' you cannot really ascertain 'evil'. Evil is the perversion of that which is good; we have, of course, the basis for what good is: God. All sin is evil because it is rebellion against that which is good, which is God.

The particular verse you referred to was referring to the Ten Commandments,

8 Owe no one anything, except to love each other, for the one who loves another has fulfilled the law. 9 For the commandments, “You shall not commit adultery, You shall not murder, You shall not steal, You shall not covet,” and any other commandment, are summed up in this word: “You shall love your neighbor as yourself.” 10 Love does no wrong to a neighbor; therefore love is the fulfilling of the law.

in which the fulfillment of the law is to be following the Ten Commandments. When Biblical verses are taken out of context, then they will cause confusion because there is no background by which to understand their meaning.

And, certainly, the secular meaning should not be used in Christian teachings; what we should be teaching is the Word of God, not the word of secularism.

When we consider the scriptures wholistically, the answer should be an emphatic yes.

Sin is transgression against the Law as David (Stratton) has said. The Law however, is not merely an impersonal and objective standard that we measure ourselves against, it is God's Law. Sin, in other words, is a transgression against God's perfect will - a rebellion against him. For this reason, (the original) David said:

Against you [God], you only, have I sinned and done what is evil in your sight; so you are right in your verdict and justified when you judge. - Psalm 51:4 NIV

The Bible makes it clear that our sin grieves God (cf. Genesis 6:5-6, Ephesians 4:30). Since the whole Law is summed up by the Great commandment (Love God etc.) and it's corollary (Love your neightbour etc. - cf. Matthew 22:36-40 as well as Romans 13:10 previously cited above), it is perfectly legitimate to view sin in terms of acting unlovingly - first and foremost against God and secondarily against others. This is a 'harm' no matter how we may wish to trivialize some types of sin and resist seeing them from this perspective. The Bible sets the ground of sin in relational terms and sin undermines our relationships. As a result, if we were to teach that some sins merely affect the individual, we would be teaching an unbiblical doctrine.

An example: It may be very tempting to want to rationalize masturbation as either not being a sin or being a sin that only affects ourself and not others. The scriptures tell us however:

Life by the Spirit

13 You, my brothers and sisters, were called to be free. But do not use your freedom to indulge the flesh; rather, serve one another humbly in love. 14 For the entire law is fulfilled in keeping this one command: “Love your neighbor as yourself.” 15 If you bite and devour each other, watch out or you will be destroyed by each other.

16 So I say, walk by the Spirit, and you will not gratify the desires of the flesh. 17 For the flesh desires what is contrary to the Spirit, and the Spirit what is contrary to the flesh. They are in conflict with each other, so that you are not to do whatever you want. 18 But if you are led by the Spirit, you are not under the law.

19 The acts of the flesh are obvious: sexual immorality, impurity and debauchery; 20 idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions 21 and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God.

22 But the fruit of the Spirit is love, joy, peace, forbearance, kindness, goodness, faithfulness, 23 gentleness and self-control. Against such things there is no law. 24 Those who belong to Christ Jesus have crucified the flesh with its passions and desires. 25 Since we live by the Spirit, let us keep in step with the Spirit. - Galatians 5:13-25 NIV (emphases added)

Most will not argue with the assertion that masturbation certainly comes under the heading of "indulging the flesh"; and it is clearly not a fruit of the Spirit - in fact, the nature of the act is antithetical to "self-control". Some may say that to call masturbation a sin is going too far as there is no explicit prohibition against it, nevertheless, my point is that whether you classify it as "sin" or something else, the fact remains that this passage strongly indicates at the very least it will be against the Spirit's leading and therefore grieving to Him - it doesn't just affect yourself.* Additionally, we often don't consider the opportunity cost of things like this - if I'm following the Spirit, then the time and energy that I would otherwise have spent indulging my flesh can be used to benefit others. To withhold such a benefit is (a seldom recognized) harm (cf. James 4:17).

At the risk of laboring the point, there is an unfortunate tendency amongst many Christians to act as though things that undermine their "relationship with God" are merely affecting themselves; this is a dangerous misunderstanding of the nature of relationships (in general, and in this case, the most important one we can have) and the truth that the Living God is a person not a philosophical construct or impersonal force (cf. Matthew 7:21-23).

*Assuming you have been regenerated.

it is reported that King David wrote the 51st psalm, after sinning with Bathsheba. Brief recap, He committed adultery, murder, and dishonored his role as the king, dishonored his parents, coveted another mans wife, etc etc.

So basically like one of the worst cases of sin "against a person" we could possibly imagine.

Yet he writes in psalm 51 3-4:

For I acknowledge my transgressions, And my sin is always before me. 4 Against You, You only, have I sinned, And done this evil in Your sight—

He says "Against you only have i sinned".

The true horror of Sin is that we are sinning against a Holy God, who gave us life.

The idea of picking how important or unimportant different sins are by how much they effect other human beings, shows extremely clearly, that in our hearts, we dont really care about God, or sinning against him.

So yes, every sin effects another person, and its the one person who really matters. God.

Jesus said, in matthew 5:27-30

27 “You have heard that it was said to those of old,[c] ‘You shall not commit adultery.’[d] 28 But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart. 29 If your right eye causes you to sin, pluck it out and cast it from you; for it is more profitable for you that one of your members perish, than for your whole body to be cast into hell. 30 And if your right hand causes you to sin, cut it off and cast it from you; for it is more profitable for you that one of your members perish, than for your whole body to be cast into hell.

I suppose we could say, In what sense? One could argue that everything you do affects other people in some way. Of course some sins afect other people very directly. If you steal from someone or beat him up, you are clearly doing him direct harm. Other sins are less direct. If a husband struggles with lust for other women, surely at some point this will negatively affect his relationship with his wife. Even if he never actually has an affair, it's got to be a problem.

That said, nowhere does the Bible define sin as things that harm others. Such a definition is too simplistic. If I owe someone money and he demands I pay, he is harming him, but I don't think asking someone to live up to an agreement is a sin. If I tried to kill someone and he killed me in self-defense -- or even just knocked me down so he could get away -- he is harming me, but that would not be a sin. You might say, yes yes, of course I mean that it is a sin to harm someone else UNJUSTLY. But then how do we decide what is "unjust"? This turns it into a circular argument: it is morally wrong to harm someone else except when it is not morally wrong.

Is it possible for someone who lives alone on an island to sin? He can't harm anyone. But according to the Bible, yes, he can. He can't kill or steal. But he could blaspheme God. He could lust. He could hate.

No, not EVERY sins affectS other people (directly, at least.).

Lust, covetousness, idolatry are three examples of sins, neither of which affects anyone else, unless acted upon.

All are sins, whether acted upon or not.

• Lust:

Matthew 5:28 But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.

• Idolatry:

Exodus 20:3 Thou shalt have no other gods before me.

• covetousness:

Exodus 20:17 Thou shalt not covet thy neighbour's house, thou shalt not covet thy neighbour's wife, nor his manservant, nor his maidservant, nor his ox, nor his ass, nor any thing that is thy neighbour's.

As for whether Christians should stop using secular definitions for doctrinal terms, from a Biblical Literalist, Sola Scriptura standpoint, I'd say, "duh!".

(No offense meant, just using that slang for emphasis. It seems stronger than just "yes")

One of the easiest way to win a debate is to redefine terms, and I've always fought back against that form of attack.

I think that from a Christian perspective, I'd sidestep the definition of "evil" and stick with the Biblical definition of "sin".

1 John 3:4 Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law

All scripture quotes KJV

Caveat:

I have to say, @user1539 has a good point.

In theory, the sins I listed are sins even if not acted on, but practically, as it applies to real-world probability and human nature, all of these would probably be manifested in some sort of way that does affect someone.

The odds that they would be "not acted on" in other words, is not very likely, and these sins would result in us committing other sins that do affect people.

So, while some specific sins may not directly affect others, they do affect others indirectly, because human nature being what it is, the sins do lead to actions that affect others.

(Although this may be splitting hairs.)

Simple: Every sin does affect every person because it weakens your faith and ability to love others. The more you sin the less good you are to everyone.