As to their motivation, I think a justification for immorality accounts for much of it. I think others are angry about their lot in life.
While I believe randomness plays an important role in reality, considering three observable facts, I don't see how our lives or the Universe are accidents. There is something rather than nothing. There are conservation laws, even if properties of various Universes are random. There is consciousness.
At the least
The atheist cannot "prove" that God does NOT exist no more than the theist can "prove" that he does. Both are compelled to assert their position without their respective proofs. To be an atheist or a theist, you have to take a leap of faith!
It is a tradgic comedy to witness an atheist assert that he has unalienable rights when the Declaration of Independence and, by extension, our Constitution asserts that these very rights come from the Creator. This Creator is the God of the Bible. This same atheist wants the unalienable rights without the Creator. He wants the unalienable effect without the unalienable cause.