The only problem with that is it assumes that the person getting killed is the one attempting to steal.
If you take away the stigma of the law and its consequences,which you would do if there was no government,how do you know that someone today who would not steal would be tempted to,knowing that he can get away with it if he kills you first.
A thief might have a 90% chance of getting away with it. Maybe a little more when he first steps into town, but less after word spreads of his crimes. It wouldn't take long for the thief's odds to catch up with him. And most would-be thieves would know that ahead of time.
If you are pointing a gun at me demanding me wallet, there is no doubt what your intentions are or who I should shoot. Same goes for if I come home and you are loading things from my garage into the back of your truck. Same if you are half in, half out of my car trying to hotwire it at 2AM. Identification is pretty darn easy from the victims viewpoint at the time off the offense.
For most people, it is our own personal beliefs and morality that define our actions. Not some arbitrary law. If cocaine were legal tomorrow, I'd still have zero interest in trying it. Same for some 90% of those out there. The 10% will do it no matter what laws you pass, so what good are they?