Some cops are decent some of the time, and some aren't.
I used to attend plenty of peace or anti-capitalist demos, not so much now that I'm a father.
Saw riot cops beating up innocent people all the time on demos.
If someone's chucking rocks at you, fine, go and get them, but don't wait an hour then go and beat up some peaceful man or woman.
Often their bosses will tell them to hold back so that the media can get their photos, and also so that the intelligence group can identify the troublemakers, then after several hours, the frontline squads are told to go clear the road or square. By then, they're frustrated after standing several hours in the heat having rocks thrown at them, so some take it out on marchers who are a completely different group of non-rock throwers.
Sometimes it's a deliberate stragety to give non-extrememe people a bad time and make them stop attending future demos, while leaving and provoking angry people into becoming even more extreme, thus splitting the movement.
One famous move is 'the kettle' - surround a group of people, about 50 - 200, and hold them there for hours and hours, till women are begging for a pee and children are crying for food and the men are reaching boiling point, then send in snatch squads to take anyone they don't like. At the end, people are released one by one after searching and photographing (illegally).
If you see a kettle line forming around you, get out quick or you'll be held in there, in the middle of the street, for the next 10 hours without food or water or anwhere to pee.
I've seen a riot cop going mad on someone who already had a broken arm and was just passing, and other cops holding the nutter cop down.
Not all cops are bad, I had a ex-cop mate, 6 foot 6, about 300 pounds, who retired after having his back broken over a railing when he tried to break up a fight outside a pub. He was a nice guy, worked in student support helping disabled students. I was still careful about what I said to him tho.
He would tell me stories about riot training - (he failed as he was too big to fit in the body armour). He couldn't accept much of what I'd seen as being true.
There's different levels and squads of cops, some are more friendly / community orientated than others.
One demo, the local riot cops who were actually quite friendly, told us that we had to stop cos the metropolitian riot cops were taking over next shift, and told us "They're real bastards, they pick all the nutters and give them trunchons and body armour and set them loose. We [local police] have to pick up all the pieces afterwards"
I've seen big men in black clothes go and smash up a Mcdonalds, with the media already waiting outside, then pass back through police lines.
That's been filmed in some places - search for "agent provocateurs police demo" and you might find some film clips.
