These large segments of the population will demand moderation from platforms they use to protect them from targeted harassment. It's these sorts of platforms that have the potential to truly become massive.
Platforms that are strongly moderated from day one (e.g. don't allow targeted harassment of minorities) don't need a "herculean effort to shift things enough to the left to be publicly palatable." A good example is the Reddit alternative raddle.me or even hacker news.