F5 is a special case here because it is the exact same action that a law-abiding person does. The reason I'm stressing the F5 case is because saying "Hey you pressed F5 with this motive, so you go to jail" is equivalent to thoughtcrime – you're being punished for your thoughts rather than your actions.

Now if someone is using tools specially built for DoS I don't have a a problem with them being prosecuted.