Mark, while it's possible that some outrageous acts "on the part of" ANY group have been done by infiltrators (or just by opportunists who have no real connection with the groups), if we are to require videotape of an incident before we can accept that it happened, there are going to be a lot of convicted criminals being set free. : )

Where's the videotape of Timothy McVeigh and Terry Nichols plotting the Oklahoma City bombing? (Just to mention one example.)

An ordained minister who is a Congressman says he was spat upon by a protestor. Extremists on all sides of the aisle have done worse, and even some of our elected officials are calling for citizens to be "armed and dangerous" (Michelle Bachman). There are posters of Obama depicted in all sorts of racist, damning ways. Why is it hard to believe that some jerk went so far as to spit on a Congressman?