The whole concept of legitimate defense is to defend yourself in a manner that is reasonnable, considering the harm that is done, or about to be done, to you.
That's correct. Therefore, if one feels that another is putting his/her life in danger, fatal force should be justified.
If a guy slaps me in the face, I can slap him back, but I cannot kill him.
A slap to the face is not a danger to life. A guy coming at you with a weapon is.
he was just vendalizing a car and he didn't seem to attack directly the lady in the car
Yeah, but he could've easily hit the lady in the car. The lady didn't know if he was going to hit her or not. One hit with a crow bar like that can kill you easily, that's why I would've shot him.
Some people are like slinkies - not good for anything, but they bring a smile to your face when pushed down the stairs