I did say "almost never," not "never." And that's true. If you look at the preponderance of cases, the vast majority of gun crimes are committed by (stand by for the shock!) violent criminals who are already legally barred from having guns. Barring law-abiding citizens from having them ability to protect themselves against people who already are not allowed to possess firearms but do so anyway isn't helping anyone. Except the criminals.
You can't solve a sociological problem by simply stripping rights away from the people who don't contribute to that problem.
I also absolutely agree that a legal gun-owner who does commit a crime should be prosecuted to the fullest extent of the law. But when has that ever been in question?