I agree with what you mean, but it's like prisoners having rights. It protects the innocent when falsely accused.
What if someone hacks your account and posts things, then you get arrested for it? You go to prison for someone hacking your account and threatening people?
What if you jokingly say you're going to kill someone or blow something up, but it's taken seriously?
This happened recently where a guy was arrested for saying "If my plane is delayed anymore I'm going to blow the airport up" on his twitter and he was arrested for it?! Even Steven Fry and Rowan Atkinson (I think it was him) made a thing out of it saying how absurd it was. But this is what these sort of laws will bring. The UN etc want this and they are using things like trolling, terrorism and bullying etc to get us to want it. If we want it, then thye don't need to force it and we have nobody to blame but ourselves.