Regarding the actions of bystanders, I was a little surprised that the female protester who glued herself to that train recently managed to escape without being relieved of jewelry and clothing, or being plastered in dog-sh!t.When the public stop believing in the effectiveness of law and order and start taking things in hand themselves there will be tears on both sides. Even if we don't agree with it (and I don't) some things are still best left to the police and courts. Mind you I suspect that setting fire to a couple of the crusties would stop the protests relatively quickly.
When people see that there is no 'official' enforcement of what many feel is reasonable, then there is indeed a danger of 'unofficial' action being taken. This will not be a poor result for those behind XR, as it will show the inherent evilness of the 'racist Nazi butchers' (aka, the general population of omnivores) and draw more support from those wavering about joining up.