No, the shoot first mentality of police and a justice system that lets them get away with it causes the "growing hostility toward police" BLM is the effect, not the cause. 

When cops can summarily execute citizens, even while being recorded doing so, and get away with it, it is only natural that citizens want to fight back. BLM and their sympathizers are trying to channel that into action that demands changes to the system, not violence, no matter what Fox and Brietbart claim. 

Law enforcement need to earn back trust. We need to stop hiring Barney Fife's that are in constant fear for their lives, and consequently shoot first. We need to do much better job of training conflict resolution and de-escalation techniques so that officers use deadly force as a last resort and not a first option. We need police to live in the communities they police and be ambassadors of peace rather than the bad "a" bullies. Time to live up to the "serve and protect" motto.