Imagine, a 'peaceful' protestor throws something, either at someone or deliberately at one of the horses. The horse spooks and throws his rider off, who is seriously injured upon landing. Other horses panic. One careers towards the barrier, behind which is a large crowd of members of the public. Because the police officers standing guard and the barrier can do fuck all against that much horse flesh, the public panic and run. People get trampled in all the chaos, possibly to death. All because the police trusted protestors to be peaceful. It could happen. With so many people present, a lot of people could get harmed if the protestors aren't as peaceful as they make out to be, or drunken idiots join in for the crack, or people pretend to be peaceful protestors but are actually there to just cause a much harm to other people are possible turn up. But hey, who cares if dozens of people get injured, possibly even killed as long as we are able to exercise our human right to protest, eh?
@Prescottdanni123 The Hollywood screenwriters have just gone on strike. There'd definitely be a vacancy for someone with your sense of drama if you don't mind crossing the picket line.