This has become a proper cause for the age and for Millenials. That is a good thing.
Historically UK has always had “groups” of discontents be they Anarchists or for example with CND " extreme protesters".
They believed they fought for a cause but they often undermined it.
#BLM is no different. It is a threat to the existing order. Some maybe 1 in 1000 will see the chance to push the anarchy agenda. Some will see the chance to infiltrate and undermine the cause.
And some may simply be Agent Provocateurs.
They damage the cause. In the US most protests have settled down and are peaceful. UK organisers should try to do the same.
The Statue defacing in London vs Bristol vs US could be down to local issues. London could be “the underminers” Bristol? That really is a local issue.
That man should not have been recognise in such a way in this modern day