Unfortunately there's always some troublemakers in the crowd that just show up for the event and cause havoc, and take away from the message of the protest and get all the media coverage. It's a shame. There are also cops out there that oppose the war and are pretty chill, then there are a lot of cops who seem to be all psyched up to kick some ass and will do so at the slightest provocation, and actually seem to look forward to protests.
All demonstrations have morons. Just like some idiots in Critical Mass who don't yield to pedestrians or bang on the hoods of cars. WTF? They degrade the core values of the demonstration and create enemies.