The people getting silenced on a privately owned platform are the ones who are saying group X should not be allowed to have any rights/exist/not be assaulted. It's not a "being racist" it's saying "lgbt people are pesos who should be beaten", "jews are in control of everything (they're not) and should be kicked out of the country". Being generically racist is clearly ok on all these platforms, its saying whole groups should not be treated as humans that seems to be the bar.
Liberal bigots tend to censor out their public statements somewhat more -- I don't believe this is an intelligence thing in as much as a learned culture, similar to the whole "being called racist is worse than being racist".
But yeah there are all sorts of double standards -- take youtube's nazis are ok, the muslim equivalent isn't, etc etc
That said the issue of censorship is always irksome to me, even if it is on private platforms, specifically how are the rules set, how do you avoid forcing stagnation...