I wouldn't be happy with it but that doesn't make it illegal. In some countries it might be considered libel/defamation depending on what was said, but those standards vary wildly between/within countries and are to my understanding generally not considered criminal

And permitting lying or misleading speech is a pretty core part of free speech, it might be socially frowned upon or disincentivised by terms of service/moderation/other methods, but it's certainly not illegal