People seem to be giving the organiser a get out of jail free card. If you are on a committee or in a group organising a march there is a lot you can do. Like kick certain people off the organisers list, like bar certain known Islamic extremists groups or members etc. Then ask the police to expel them if the turn up. Some protest have made statement ahead of the marches to just use the pre designed signs and about behaviour. Which is good. That should happen every time.
Also when behaviour happens on protesters that is dodgy or violent the organisers need to call it out and condemn it at the time and after the marches. Plus others protesting need to learn to do the same. That is the only way those on protests to act verbally or physically violent or promote such behaviour will learn it doesn't fly with everyone eles. That will seriously clean up the image of these protests.
Oh and don't protest outside people's houses or religion places or try to do convoys through Jewish places. Keep it to political offices, businesses and organisations etc. Not personal addresses.