The existing practice is for the community of these sites to upvote good content and downvote bad content.
Separately, moderators purge controversial content as a check/balance to the voting system. If users feel that the moderation is inconsistent with their content desires, they choose a different site to frequent, as is the case in market systems.
again, if you look at the whole system in aggregate, the existing practice is for GooFaceTwitBaba to farm out their moderation works to subcontractors, while also bending backwards to prevalent political headwinds to preserve their shareholder value. If users feel that the moderation is inconsistent with their content desires, they are free to leave the megaplatforms and become approximately completely irrelevant, thus achieving the exact same effect as being deplatformed.
Separately, moderators purge controversial content as a check/balance to the voting system. If users feel that the moderation is inconsistent with their content desires, they choose a different site to frequent, as is the case in market systems.