I guess the common through line is bigotry. Whether it’s directed at Christians, Muslims, women, gays or trans, it is all the same to him.
You're surprisingly close to the mark. Bigotry is an ugly word for it, but there is a human tendancy to view the world as in-groups and out-groups. The groups that we're a part of are better than those other groups and anyone who says otherwise is an idiot.
Anti-theists thrive on being superior to people who believe in religion. It's not a big jump to replace those religious people with a different outgroup. Being superior to gay people or women or people who like marvel movies satisfies the same base need to feel better about yourself by looking down on someone else.
Lemmy's simpler algorithm still has the same the problem though. That's been seen time and time again on Reddit. Humans will actively curate a feed of content they find engaging and avoid content they disagree with. This leads down exactly the same rabbit holes as if you let an algorithm curate a personalised feed for that user.