That's part of the Sophie's Choice. If we have private owned social media, then they will moderate according to public opinion. If we have us government run social media then we have no moderation at all because 1st amendment applies only to us government.
So is it morally allowable to discuss <abhorrent topic> online? Should it be law to allow or disallow <abhorrent topic>?
Who decides what the majority of people consider to be abhorrent?