Blackshaw at least (because he actually showed up for his planned riot, the other chap didn't) would go to prison if he did this anywhere in the world. Even in the USA with its extremely strong protections for speech, inviting people to meet at a set place and time for the purpose of rioting is illegal.
Even Sutcliffe-Keenan (who at least was smart enough to delete his event from facebook after he sobered up) basically did the equivalent of calling a bomb-threat.