The problem isn't that they're scary or compelling but that they bring discourse down to its basest level once they comprise a certain proportion of the environment. Imagine if 90% of HN threads were mostly just discussion about if the author of a submission or comment is Jewish, what their ulterior Jewish motives are, and what repercussions they should face in an ideal world. Many clusters of Twitter are now that.*

A lot of people see the culture shift and start posting less or leave, and then the ratio gets worse and worse. Freedom from government restriction of speech is a good thing, but I disagree that this new era calls for throwing out norms of discussion platforms curating their communities' cultures.

I fully acknowledge there are valid, interesting philosophical reasons to host a site like Twitter or 8chan where "if it's legal it's allowed", but on net I think the benefits do not outweigh the costs.

*(Even many 4chan boards are less obnoxious. In part due to its linear format.)

You’re speaking for yourself now. Millions of [mostly russian but not only] people today are convinced that the extermination of millions of Ukrainians is the morally righteous course of action.

Populations being persuaded into harbouring extremely bad ideas is a thing.