There is a meme something along the lines of "given enough time, any community will turn right-wing without heavy left-wing moderation".

I'm inclined to agree; it's not about the website format so much as how the admins/mods handle the community. See Twitter vs the various twitter clones, or reddit vs communities.win - the websites are designed almost the same, but the moderation policies are totally different, so the communities end up totally different.