Well it is the police's job to arrest them. It isn't their job to be judge, jury and executioner. I have no problems with police killing someone if they resist arrest and shoot at them. I do have a problem with police setting up an ambush for criminals and gunning them down with no attempt to offer a chance to surrender. That's fundamentally against the way our justice system is supposed to work.
By your reasoning police should have almost unlimited power in certain situations. I don't care to live in a police state.