You hit the nail on the head with the point about them feeling a moral obligation to control. They operate upon the politics of disgust. This is disgusting, it should not exist, no one should ever think about, see it or even acknowledge it's existence. But disgust is so personal, so subjective. Person A is disgusted by Hydra Trash party fics. Person B is disgusted by the existence of trans people. Person C is disgusted by the mere idea of casual sex for pleasure instead of marital sex for the purpose of reproduction. Person D is disgusted by the existence of queer people. Person E is disgusted by interracial couples. Who gets to make the rules about which disgust is valid and which disgust is OK actually?
You can't base rules on such a shaky foundation. Disgust, like any emotion based system, is too fluid and too subjective to be a useful measure.
AO3 does not host illegal works. Despite the frothing claims of puriteens and the anti mob it is not actually a hotbed of pedophilia, bestiality and necrophilia. It's not a pipeline to having the moral fortitude of boiled pasta. It doesn't normalise any fucking thing, you rabid dingbats. You want the archive of moral purity and wholesome fics only? Do it. Go ahead, noone is stopping you. Put the energy and drive you are wasting in a useless crusade into forging the purity prevail archive.
Rally your pearl clutching feelings yakuza friendship groups and do something constructive instead of performative slacktivism. The archive was formed by fan groups wanting a safe space to store and share their fics. Literally nothing is making you use AO3 if it's so distasteful for you. Good luck with your pristine purity Archive with added censorship and malleable moral boundaries. You will all be a bit busy prechecking every word prior to publishing and actually I think it would be great for you to be so busy with the stuff you care so deeply about.