Well there is /r/BlackPeopleTwitter, which generally has a lot of vitriol aimed at white people which goes wholly unchecked.

It is also the home of "country club threads", wherein you're banned from commenting unless you are a PoC or have proved yourself to be a "white ally" (initially I think it was only PoC and none of the white ally stuff, but they let them in later in response to continued backlash – also because I think many of the mods aren't actual PoC so looked even more ridiculous than it was already).