I'm not sure I agree that everyone who defends himself with a firearm should bear the cost of defending against a capital crime. Obviously, some should.
I've been a fairly strong proponent of gun ownership, mostly on the theory that a right to self defense is pointless without a means to defend oneself. On the other hand, I have known several people with multiple guns who can talk themselves into a frenzy describing what their particular ammunition will do to a person, and how they're going to react to their unlikely scenarios.
There are people actually hoping they can get into a situation that lets them somehow 'prove' themselves. They're not convicted felons, they have not been adjucated mentally incompetent, and they're as legal as you or I.