What legal actions could anybody went after? They don't allow illegal activities and don't even allow interaction from the site. Even talking about it is banned. Why do you think so many attempts to take them down have failed. They follow the law and openly work with it if something illegal does happen... Including the FBI.
And in the context of KF, harassment and even interacting is against the rules. Attempting to do anything illegal, making threats or swatting etc are literal instant bans with your info being handed over to law on request.