The burning of a Guy Fawkes effigy has been a political statement for centuries. It is a statement of disapproval and the same is true of contempory politicians who find their image being burned.
There is no comparison with a bunch of far right nutjobs revelling over the deaths of 72 men, women and children. Making fun out of a large scale tragedy, and laughing at the real victims is horrible in the extreme.
Burning a likeness of a politician is no worse than tweeting disapprovingly about them. It is just a comment of current affairs.