Time changes, and the rules change with them. When I was a LEO many, many, moons ago, I was trained in this manner; Never pull your service weapon unless you intend to use it, and when you do shoot to kill!
As a retired old fart my rule today is; Never pull your gun unless you, (your family / friends) are threatened with deadly force. Be calm, be cool!
As a realist; you can never be sure what you will do in a deadly force situation. If you make a mistake; there by the grace of God, go I!