<< can't u try to disable the person nonlethally by aiming at the leg/arm, or knocking him out with a spray/taser? >>
Folks, this ain't the movies, and you ain't Clint Eastwood.
Self defense situations happen in mere seconds. For all you "why not just shoot him in the leg" folks, go to a firing range, lay the gun down on the table in front of you, pick it up and fire it once at a target 15 feet away in less than two seconds. Now, tell me if you could reliably hit a leg or an arm (Or even the head for that matter) in this situation.... and remember, you'll be under a LOT of stress, and your target will likely be moving. This is the very reason police are taught to always aim "center mass." You have the best chance of a hit if you aim for the chest.
Police also aim center mass because it has the most stopping power. The whole point in shooting an attacker is not to kill, but to insure he will not continue his attack. People on drugs have been known to continue attacking an officer after being shot multiple times. With this being the case, a leg or arm shot is even less appealing in a self defense situation.
Your attacker is NOT going to give you a second chance. He's NOT going to stand still to allow you time enough to aim at something as small as a thigh or calf, and he's NOT going to react kindly if you miss. Your only defense is to NOT MISS, and your best chance of not missing is to aim square in the center of his chest.
To answer the question, yes, without a doubt I would use lethal force to protect myself and/or my family.