Popper's Paradox of Intolerance is the main reason that online platforms need moderation of some kind:

The paradox of tolerance states that if a society's practice of tolerance is inclusive of the intolerant, intolerance will ultimately dominate, eliminating the tolerant and the practice of tolerance with them. Karl Popper describes the paradox as arising from the fact that, in order to maintain a tolerant society, the society must retain the right to be intolerant of intolerance.

We have seen this happen again and again in comment sections, where moderation was removed and the platforms were taken over by trolls and bigots, driving out those people who wanted to engage in real discussion. I saw this happen with the Yahoo Message Boards in the early oughts, and were watching this happening real time on X.