Well, you go right ahead and keep your weapon in a functionally unloaded condition (round not chambered) if that's what you're comfortable doing. What you are ignoring, however, is the very great chance you will be stressed if you wait to chamber a round when actually faced with a threat. That's when you'll likely cause a feeding malfunction and have to clear the gun before being able to chamber a round and be prepared to fire.
Work on your handling skills, learn your weapon and apply the four rules of safe gun use. The Ass't DA in this situation obviously violated all four rules. The gun wasn't at fault, he was IMHO.