Latter-day Saint understanding of James 1:13-15, God's omnibenevolence and God's free will?

Greek

The punch line of the OP is a question about Greek more than a question about theology.

The word often rendered in English as "cannot be tempted" is ἀπείραστος, which occurs only once in the New Testament and never in the Septuagint. The alpha is a negative prefix affixed to the word πειράζω. The verb "can" is nowhere to be found; it is supplied by the translators (in some cases).

The same word (πειράζω) is used by the same James in Acts 15:10

Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear?

It is also used in Hebrews 3:9, quoting God as saying:

When your fathers tempted me, proved me, and saw my works forty years.

Furthermore, that God can be tempted is explicitly acknowledged in Deut. 6:16

Ye shall not tempt the Lord your God, as ye tempted him in Massah.

In this latter example, we have God acknowledging that God was tempted.

However, if we remove the idiomatic translation in James 1:13, there is no contradiction here. As explained in Benson's commentary on James 1:13

Here, to tempt, signifies to solicit one to sin, and actually to seduce him into sin, which is the effect of temptation or solicitation. See James 1:14. In this sense the devil tempts men. And because he is continually employed in that malicious work, he is called, by way of eminence, Ο πειραζων, the tempter. It is in this sense we are to understand the saying in the end of the verse, that God is incapable of being tempted, that is, seduced to sin by evil things

That people can (and have) tested or challenged God is demonstrated many times in the Bible: but He passed every test. People tried to get God to renege on His promises and that game never worked. The same concept shows up in the other direction in Malachi 3:10 where God challenges people to put Him to the test--to try out His promises and see them fulfilled.

Greek Conclusion

Translating James 1:13 idiomatically to claim that God cannot be tempted (or tested or tried) makes James contradict his own statement at the Jerusalem conference (see Acts 15 quote above). Rather, what James establishes is that no temptation levied against God will be successful. God will not be seduced or tricked.

Logic

In my linked answer (Answer2) to the antecedent question, I accepted premises 1 & 3, and I rejected premise 2. I did not take a position on premise 4. Another answer had already challenged the OP on the matter of (potentially) switching definitions between premises, and I did not explore the matter further in my post (save for a comment that I had qualms with the presentation of premise 4).

I am not convinced that "capable of moral evil" is being used the same way in premise 4 as it was in premise 2. If premise 4 adopts a novel definition of "capable of moral evil" then the argument is not logically valid. Since the terms were not defined and I was left with some uncertainty, I didn't take a definite position on the matter.

A few of the questions that occur to me are: how are we defining moral evil? Are acts of omission potentially morally evil? Is choosing anything other than an optimal outcome (or choosing nothing) morally evil? Is Divine Command Theory in or out of scope?

Capable

What is meant by capable?

Derren Brown's show Pushed to the Edge (aka "The Push") is a recent effort at exploring this question. In this "reality tv" drama, an unsuspecting participant is surrounded by actors who will put the participant into increasingly stressful/compromising situations and try to convince him to push another human being off a roof to his death. The pushed individual actually has a harness and will not be harmed, but the pushing individual does not know this. If persuaded, the pushing individual will have made a decision to commit murder.

Whether or not the whole thing was staged is another matter. The question presented to the audience of the show is whether a person can be manipulated into deciding to commit murder.

That one human being is physically capable of pushing the other human being is obviously true. The sinister question Derren Brown explores is whether the one human being is psychologically capable of pushing the other human being. Both are questions of capability, but they carry very different ramifications.

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One other brief matter with respect to James 1:13 -- aside from the discussion of Greek above, I see a logical gap in the argument:

The OP suggests that If, according to James, God cannot be tempted by evil, that explicitly contradicts the belief that God is capable of moral evil. How so? That only holds if it is impossible to do evil without first being tempted. There may be good reason to conclude that such is the case, but none was presented (e.g. for an interesting counterexample, Satan does moral evil all the time--is someone/something tempting him?).

Logic Conclusion

What we mean, then, by "is God capable of committing moral evil" is not so clear cut. I found premise 2 of the original argument straightforward to refute because it misused the meaning of omnibenevolent, but in hindsight, my answer would have been stronger had I discussed what I understood the words to mean.

Theology

I do not speak for all Latter-day Saints (presumably the statement in the OP they believe that God is capable of moral evil uses "they" to refer to myself and Mason Wheeler, not all Latter-day Saints). Christian denominations tend not to make doctrinal pronouncements on deeply philosophical questions unless they believe they have an authorized source supporting that pronouncement. My own church's Articles of Faith cover matters much more relevant to human salvation.

That is to say, my comments here are speculative and a matter of personal opinion.

My read of the scriptures is that when we are told "God cannot do X" (e.g. Titus 1:2 - God cannot lie) it is an acknowledgement of God's perfection, not a philosophical treatise on free will (or omnipotence). God is consistent and reliable such that "He can't do X" is but an emphatic and entirely assured statement that "He won't do X".

I've heard it said that mature love in a relationship includes (but is not limited to) knowing exactly how to push someone's buttons and choosing not to do so. I see that God exemplifies this principle.

Theology Conclusion

God sticks to His principles 100% of the time. So even if He physically can do something that would violate His principles, He doesn't. And He promises that He never will. We can't independently fact-check Him on this--we can either choose to believe Him at His word or not. God has given me clear reason to trust Him, and I take Him at His word.