'x is illegal' is a cop-out (albeit often unintentional) and I wish people would stop using it.
anything can be made illegal, are you just going to roll over if expressing an unpopular idea becomes a crime? Conversely, illegality doesn't deter a lot of people and many are skilled at playing with the envelope of legality, so absent any moderation you'll get lots of technically/arguably legal content that is designed or degrade or disrupt the operation of a target forum.
It's unhealthy to just throw every difficult problem at courts; the legal system is clumsy, unresponsive, and often tends to go to unwanted extremes due to a combination of technical ignorance, social frustration, and useless theatrics.