Yes I do. But I think that has more to do with their nature than the actual vitriol (barring posts that encourage actual violence). Like
@Jeremiahcp said, the vast majority of people reading this stuff aren't inspired to go on a shooting spree.
So, while the vitriol may focus this person on a specific target, I don't think it's the actual cause.
Do you think that we should silence vitriolic political speech because there are some people that may become motivated to act upon it? That seems like a dangerous slope to me. And not to mention, what about everyone else who can partake without becoming violent? It's like banning steak because babies can't chew, or so the saying goes.
While I haven't actually watched any ISIS videos (yikes!), I assume that they are encouraging people to perform violent acts. As mentioned before, I think that does cross the line. I think encouraging or suggesting that people go shoot up Congressman can be linked to causing people to actually shoot up Congressmen.