It is censorship, though. Not government censorship, but don't you think that one day in the future, once these non-government censorship systems are in place, that a corrupt or evil government could abuse those systems and make them defacto government censorship systems (we're already partway down the slope with things like CSAM and copyright monitoring, although the former is especially heinous and so censorship of that type of content is desired).

Not every provider of user-generated content should have to abide by these rules, because the damage that can be done by a relatively small forum or website is usually minimal (although see sites like Kiwi Farms that may not technically directly encourage harassment but where it is nonetheless often perpetrated by sadistic individuals who participate in their forums), whereas the damage that can be done by a Facebook or a Google is much, much greater.