for example, if I substitute every reference to the superiority of atheism to theism (or the inadequacy of theism more generally) with a similar reference to the superiority of, say, heterosexuality to homosexuality (or the inadequacy of homosexuality more generally), my emotional response is basically "yeah, fuck that shit."

These examples are not at all analogous. Claims about the existence of divine agents - or the accuracy of old textbooks - are epistemological claims about the world and not up to personal preferences. What do I know and how do I know it?

Claims about preferences can by definition not be objectively right or wrong, but only be accurate or inaccurate relative to their frame of reference, to the agent they are ascribed to. Even if that agent were some divine entity. Jesus would like you to do X, but Bob wouldn't.

Or, put differently:

"There is a ball in the box" - Given the same evidence, Clippy and an FAI will come to the same conclusion. Personal theist claims mostly fall in this category ("This book was influenced by being X", "the universe was created such-and-such", "I was absolved from my sins by a god dying for me").

"I prefer a ball in the box over no ball in the box" - Given the same evidence, rational actors do not have to agree, their preferences can be different. Sexual preferences, for example.

The reason that theists are generally regarded as irrational in their theism is because there is no reason to privilege the hypothesis that any particular age old cultural text somehow accurately describes important aspects of the universe, even if you'd ascribe to some kind of first mover. Like watching William Craig debates, who goes from some vague "First Cause" argument all the way to "the Bible is right because of the ?evidence? of a supernatural resurrection". That's a long, long way to skip and gloss over. Arguing for a first mover (no restriction other than "something that started the rest") is to arguing for the Abrahamic god what predicting the decade of your time of death would be to predicting the exact femtosecond of your death.

Such motivated cognition compromises many other aspects of one's reasoning unless it's sufficiently cordoned off, just like an AI that steadfastly insisted that human beings are all made of photons, and needed to somehow warp all its other theories to accommodate that belief.