Did you hear the 911 call from the granny who shot an intruder? All I can say is "you go girl". I think that if you shoot someone for knocking at your door and there is no evidence that there was a real threat, you WILL be prosecuted. I think the law will not be so lenient that trigger happy people are let off.
Oh, and as for knocking on someone's door in middle of the night... I wouldn't do it because THEY may be the bad guys. You never know whos door you will be knocking on. That is why I carry a cell phone, although we were chased by bad guys through the smoky mountains one time and could not get a signal. Praise the Lord that they gave up when we got to Gatlinburg. Oh, and if dh had had a gun, I personally would have leaned out the window and shot until the gun was empty. They were trying to run us off the road at 11pm at night. We had a van full of little ones and there were two of them. You bet ya there would be 2 less criminals in the world today.
In Louisiana, I was always told that if you shot an intruder, just make sure he falls INSIDE your home. I don't know for sure what the law is/was, but was always told that you only had the right to defend yourself, not your property. Don't know if it is still the same. Now, I don't know if it is right to shoot someone who is leaving your home with your car. It is just a car, sure the thief is wrong, but I don't think death is a fitting punishment for that. The bible allows a life be taken in defense of life. When it says thou shalt not kill, it does not mean never under any circumstances. God makes it clear that you can defend yourself. As for defending property I don't think that is the same thing. Now, if he is taking your car and trying to run you over, shoot to kill. I also don't think you should shoot someone who is fleeing.
Now, knowing many people who own/carry guns. Those are the people who have and use common sense. They treasure life and will not use deadly force unless they truly believe it is necessary.
Oh, I do think it would be OK to shoot him in the thigh if he is trying to steal your car though. But then of course you run the risk of him suing you. We really need to fix that loophole. If they are shot on your property, but don't die, they can't sue.