As far as I can tell this is just far-right propaganda to disguise what actually happened -- which is the UK imprisoning people for conspiracies to burn down hotels with immigrants in them; or participating in on-going violent riots by calling for various buildings to be attacked or people to be murdered.
This speech isnt covered by free expression, and is a crime in all countries, including the US.
> David Cameron is a twit
Not
> I'm going to blow up the airport
Can't imagine why this person got jail time for that given that it was just idiocy, but still
Lots of "idiocy" is explicitly illegal. Being dumb isn't an excuse to commit a crime. Literal children in the US get in trouble (legally, as in, sent to juvie) for bomb threats all the time.
Making a bad judgement call, like "surely everyone will understand I'm just joking about my threat to literally murder people" often has legal ramifications.