Or they oppose feminism because they favor #WhiteSharia (or normal sharia) or pathologically hate women. These men aren't the majority of men, but they can be the majority in certain e-forums.

I don't begrudge these men the ability to have their own spaces. I would defend /r/incels or /r/islam against censorship, but I wouldn't expect fair, equal moderation if I posted there. From the dawn of reddit (and the broader internet before it), mods could curate their own private discussions. The issue is when you try to interfere with other peoples' discussions, or when you unfairly moderate a forum that purports to be neutral and open.