Barry - Yes the punch is 'understandable' but 'understandable' does not mean 'acceptable'.
I have less than no sympathy for these people.
I think they are attention-seeking seeking idiots, their cause is bogus, and their actions to support it are indefensible.
But, as Deskdiary points out, how long before we start saying that GBH is 'understandable', and then life-changing injury, and then death.
We have to stop at the beginning of that road, and that is where we are, because we are supporting lawless behaviour as a response to lawless behaviour, and that will only drag us into a vigilante culture.