Protecting personal property doesn't give someone the right to kill, the two are very different things. If it's a choice between someone stealing my car or killing them how can anyone justify that!
In many jurisdictions citizens are allowed to use lethal force to protect their property, which often includes preventing someone from entering their premises with the clear intention to steal or destroy their property.
In the case of a mugging, where the perpetrator is using physical force in an attempt to take your purse, wallet, computer, etc., out of your own hands, you are generally allowed to use lethal force to stop him.
As for your car, given the dismal financial situation which you so often brag about to us, I'm sure you drive a 1972 Datsun. Anybody who's so desperate that he would steal that car may perhaps deserve your mercy. But most of us drive a car with a five-figure price tag. Our insurance policies clearly state that if that car is stolen or destroyed, the insurance company will only pay us
its wholesale value. For many of us, that's not even enough money to pay off the loan. It certainly won't buy a replacement of equivalent value. You pay $30K retail for a car (which these days isn't even a particularly fancy one), somebody steals it, and you get wholesale bluebook which would be around $25K if you're lucky. You're immediately out $5K, and you have to pay to rent a car for a couple of weeks while you find your next one--for which you'll also pay another thousand bucks for tax, license, emissions inspection, yatta yatta.
Not to mention, everybody's car is full of extremely personal stuff. To have your car stolen is like somebody breaking into your house and looking through all the drawers in your bedroom and your office, and then dumping it in the street.
I'm a pacifist but I'm also a firm disciple of situational ethics. If somebody's going to do that to me, then as far as I'm concerned he has removed himself from the structure of civilization. He's just vermin, and vermin can be exterminated. I don't have a gun (statistically I'd be three times more likely to shoot my wife than a burglar) but I'd certainly run him down with my 5000lb car.
And then I'd back over him a couple of times just to make sure.

(Just kidding. I'd let my dogs take care of him until the cops showed up.)
We live in the most generous country on earth. People move to Los Angeles just because the weather is so mild that they can sleep outdoors 340 nights a year, and the people there are so politically leftist that they give money to panhandlers all the time. Even drug addicts can get free help.
Nobody in America is so desperate that they have to steal somebody else's stuff to survive. They're just lazy, or greedy, or selfish, or their momma didn't raise 'em right.