When a leftist says "X is violence", they aren't saying "We all need to stop X because violence is wrong." Leftists are just fine with violence for the right cause. Those pearl-clutching statements are virtue signals to other leftists that "X represents a danger to our movement and needs to be shut down."

It's a power play disguised as a moral plea. The same rule applies to attempts to limit hate speech or use PC language for sensitivity reasons.