There will ALWAYS be a small element looking to hijack theses protests to satisfy their own anarchic needs.
The thing that winds me up so much is that they really are a very small minority, but television, newspapers & the internet spend so much time focusing on that minority, it does nothing but give them the exposure they so crave.
Let the police do their job. Don't rise to the "vermin". The more uproar they receive from their actions, the more they'll do it.