This is the kind of outcome Section 230 (of US' Communications Decency Act of 1996) was intended to prevent.

It's an unpopular opinion in tech circles, but this right here is why I support the very maligned Section 230—in fact, I wish it'd go much farther. I think it's a core human right to talk on the internet and to create websites: a right that should be protected, in practice, by granting powerful immunities to third-parties, like forum administrators. Else you end up with chilling effects like this one, chilling things no reasonable free society would want to chill.