Well sure you can take it to one extreme and say "I could get arrested for making a joke", but I could take it to the other extreme and say "we can never preven

Well sure you can take it to one extreme and say "I could get arrested for making a joke", but I could take it to the other extreme and say "we can never prevent terror attacks because they can't be arrested until after the attack". I'm not a lawyer or a policeman, I've no idea exactly how it works, but I know I would rather murders are prevented than just punished after, and I would rather people planning on setting fire to London are prevented rather than just punished after.