It shouldn't cause the perp was not actually part of the peaceful protest but you're right, it will overshadow it.
How does it hurt the cause and what cause? They're remembering the life of a thug armed robber. They're simply celebrating in Michael Brown fashion. If he were alive today he would be out there lootin' and shootin' with them!
Wish I had a link but ooooooh ooohh this guy sitting in for Bill O'reilly just had this black sheriff from Milwaukee on and he just straight up blasted these fools in Ferguson. Called them a bunch of race hustlers and said they had a phony movement (black lives matter) this cat is real. Put that dude up for Prez!