Exactly right!
"Proportionate" has an air of "break-even" about it which can be a sucker bet, in this case for the public.
There is simply no way to know the extent of damage caused when a violent group disturbs the peace and shatters the ordinary course of civil events. Beyond collateral physical damage there are such things as the cancellation of graduations, etc.
Aggressive protests diminished significantly after the Kent State shootings, when protesters realized that they were throwing stuff at armed men with loaded weapons.
Protests would stop if riot cops waded in with batons, and broke bones and skulls. But the cops know THEY would be heavily prosecuted by the same DAs who release the protesters without charges or bail.