Well, there are definitly some different sensibilities between the US and the UK regarding free speech. To any extent that someone should be imprisoned for something like that should be because they were orchestrating the riots BY their speech, not the speech itself.
The facebook riot teenagers didn't just say 'we should riot' or something like that. That might well be protected speech. One of them set up a facebook event called 'Smash Down' and basically attempted to organize a riot by getting supporters to meet at a local McDonald's restaurant (I believe that the only people that showed up was the teenager himself and the police).
Someone else did something similar, setting up a page called "Riot in the toon" (toon meaning 'town' generally referring to Newcastle where their accent causes 'town' to be pronounced 'toon') with an incitement for people to "kill some daftys" (a dafty, I believe, is someone who is daft). That person had previously lead a small civil disturbance of about 30 youths.
There were some other similar cases too, I believe.
From the limited information I have the priest said that it
quote:
gives a man the absolute license, without limitation, of abusing the body of this woman because she is the tragedy that brought you, and brought it as if it were a right
It's a google translation from Portuguese, but I think the meaning makes its way through well enough.
So I wouldn't necessarily regard this as incitement in the same way the Facebook cases might have been, it's 'just' rape apologetics.