I don't see the cyclist in the wrong here. Most traffic laws classify cyclists as motor vehicles regardless of any minimum speed in the city/state you're talking about. If you bike on the sidewalk, you can get a ticket for it in WA state. If you bike in the road, you risk being struck by vehicles (you always lose, regardless of who's morally or legally right if that happens) and you can impede traffic when motorists don't know how to drive around cyclists or feel they can't.
It's just incredibly hard trying to balance the needs of pedestrians, cyclists and motorists on our roads and trails so there's a lot of conflict and anger between the different groups. The thing that really stands out for me on that video clip and the article attached to it is that the cop basically body-checked the guy off the bike and then wrote in his report that the cyclist ran right into him, causing them both to fall down.
The cyclist was thrown in jail for 26 hrs without hospitalization and charged with "attempted assault, resisting arrest and disorderly conduct". The cop's been stripped of his badge and put on probation pending an investigation that started after that video showed up.
It's not right to clog up the streets with an 'unorganized' march like this without a permit (although it's debatable if you actually need one depending on what city/state you're in), but that doesn't excuse the cop or anyone like him in law enforcement not doing their sworn duty to protect the law and the people by acting like the guy did.
This video is not funny. Don't laugh at it.
Edit: Did some more poking around, go read this:
http://gothamist.com/2006/01/11/judge_says_bike.php if you still think the cop's justified here.