Currently, it's quite difficult to convict somebody of incitement -- especially when the waters are muddied by political rhetoric. Whether it should (or shouldn't) be is another issue.
As to leftists, I think more and more of them have started to see violence as an answer -- but only for the "right" people. The OK-to-punch-a-Nazi phenomenon verbalized (picturized) a sentiment that, in my opinion, has been breeding for quite some time, particularly on college campuses.
This young woman was pepper sprayed because she wore the wrong hat and played for the wrong team; all she was doing was giving an interview. The thing is, these people view their actions as a form of self-defense. They stopped buying into the whole marketplace of ideas thing we've historically adhered to. Bad speech isn't something to be countered; it's something to be
made to stop, as it represents "violence" against them.
Personally, I don't think these sorts of people have any business being near the legislative pen should we start re-defining what incitement is. We go down that road, there's a fair chance they will be.