Why? Becasue what's going on for hours and hours beforehand is really dull, and forcing thousands of people to watch that would be a really dick thing to do. If you dig, you'll find that longer clips are available, but they don't actually add anything to the discussion other than "nothing happened to provoke the police".
If you're going to take a karma hit, it's because you're posting nonsense, and putting quotes around the police's brutal, unprovoked aggression doesn't make it something else or justify it. It does, however, make you look like an apologist, or secretly a member of the NYPD.
As for intending to provoke a police response, that's wrong on so many levels I'm not sure where to begin, other than to say you sound really paranoid. You could just as easily say, "in the thousands that are there, you can't say there aren't any police agent provocateurs."