Tim, I will stop responding to you after this, so feel free to have the last word. But let me just reiterate once again that Nagasawa’s article does not provide any model of atheist cognition, so your criticisms are off base. There are different studies that go in that direction - but, researchers of atheism would emphasize there is probably no single model of atheist cognition, just as there is no single psychology of religion.
I will also submit an alternative explanation for why the existential problem of evil, as it relates to evolution, does not bother people more. Most people probably just do not really believe that nature is evil or that the existence of animals is overall bad. This just does not match most people’s experience of the world, and their awe and appreciation of animal life. Thus, the most pessimistic views become simply a theoretical problem that some people use to criticize theism, in a way that is inconsistent with many of their other beliefs and behaviours, such as gratitude for existing etc.
However, if the most pessimistic descriptions of evolution were correct, then I would continue to think that really believing in them would have a psychological cost. Then, we would be living in something surprisingly close to a lovecraftian universe. Here’s how H. P. Lovecraft put things in The Call of Cthulhu:
The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents. We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far. The sciences, each straining in its own direction, have hitherto harmed us little; but some day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the deadly light into the peace and safety of a new dark age.
So, as a thought experiment, let’s suppose we live in a lovecraftian universe, where the old gods from Cthulhu onwards exist (so, the world is hostile, evil, ugly, horrifying, cruel, indifferent to human and animal suffering etc. as stated in the most pessimistic description of evolution). But yet, most people live their lives gratefully, optimistically, etc. I would submit that the most plausible explanation for such existential optimism would be just that most people do not really know or believe the world is evil - the knowledge of Cthulhu is just too remote and difficult. But, I would also agree with Lovecraft and Nagasawa that for those who do come to believe that the universe is hostile in this way, this will have psychological costs and present a challenge of existential evil. Once discovered and really believed, we cannot just ignore the existence of Cthulhu and go on as if it makes no difference.
Anyway, in our actual world Cthulhu does not exist, and neither does evolution add to the problem of evil. And that also helps explain why people are not concerned that much with these particular existential evils. There are plenty of other, real existential evils though - I would (perhaps unsurprisingly) start that list with human sin and death rather than evolution. But, that would be a separate conversation.