An atheist is a materialist. For him the only thing that exists is the material world. While we can wonder about why this or that being is the way it is, questions about what causes the material world as such are nonsensical, as are questions of its meaning and value, which imply finality.
So the atheist should be neutral on moral questions: sure, he might think one choice or another is more or less convenient for one’s provisional goals, but there is no way of knowing the long-term effects of our choices and in the end we are all just cosmic accidents waiting for entropy and extinction.
But that does not prevent individual atheists from holding incoherent positions. You might for example find one who believes strongly in animal rights or in feminism, which are absurd ideologies when considered in the grim light of the cold, uncaring gears of the universe ticking away towards the eventual destruction of our species.
Who’s saying an animal does not regret killing? Who’s to say they do not loathe having to do it? [… they are] free to recognize and be utterly appalled at this existence it has found itself (uninvited) in… a world where every creature is contracted by birth to prey upon the other in order to steal the proteins and fats and sugars and minerals they need just to stay alive one more day in what amounts to a daily apocalypse of obliged bloodletting.
Besides the false assertion that predators do not enjoy hunting and killing – a few days spent in the company of a terrier or tabby-cat will disprove that – the mental image of wolves and sharks feeling tortured by existential angst for their places in the food chain is laughable.
This is not the ontological indifference one would think proper to atheism, but full ontological pessimism: nature is evil. It is a position proper to the dualistic religions of the ancient Middle East, which saw creation and matter as evils to be escaped.
The context of the comment was the question of why God created the world. The general discussion was a failure: I could not convince him that there is no contradiction between a perfect God creating a imperfect world, and he could not convince me that there was.
Then came this utterly bizarre turn towards ontological pessimism.
I have an hypothesis as to how someone can argue themselves into this position: there is in fact a popular atheist apologetic trope that runs something like this: how can a good God create a world which contains so much evil? God must logically will that evil exist, therefore he is not good. But if God is not good, he is not God. Poof! God disappears in a puff of logic.
But while the atheist apologist is making this argument he is supposed to have in the back of his mind the realization that he is only employing the terms “good” and “evil” to create a dilemma for the believer. The atheist himself does not really believe in good or evil in any absolute sense. The goal is not to convince the believer of the evil of the world – that would be silly – but to ultimately convince the believer that the entire edifice of creation, God, matter, good, evil, finality, etc, is absurd and should be abandoned.
So it might be that while trying to convince a believer of the wickedness of the material world, the atheist apologist really starts to believe it himself.
In which case he would be better off becoming a Hindu.