/r/Christianity - run by Protestants where even questioning liberalism (acceptance of active gays, transgenders, female 'priestesses', liberalism) and advocating for any traditionalism will get you shut down fast. I've been banned there on like 5 accounts.
/r/OrthodoxChristianity - the forum would be OK if it wasn't run by a leftist woman. She puts her agenda in front of everything, so more traditional Eastern Orthodox people get shut down fast, as well. She's a real cunt, that one.
/r/Catholicism - the only forum on the internet I really enjoy. The mods there are priests and seminarians. They're as traditional as Catholics can get and it's the opposite of /r/Christianity, where any liberals get shut down ASAP. If you go there, expect traditional Catholicism.