I imagine the police are standing aside for the same reason they're standing aside as people tear down all sorts of stuff - safety. It's just not worth getting people hurt over stuff.
It's easy to fix a mural, or replace a statue. It's just a thing, right?
I really don't think we want to encourage brawling over public art installations. It didn't end well in Albuquerque, and it probably won't end well anywhere else.This calls for a citizen's arrest!