Geezus, you just don't get the concept behind self defense.
Here, from Findlaw....
What's an affirmative defense?
An affirmative defense is a justification for the defendant having committed the accused crime. It differs from other defenses because the defendant admits that he did, in fact, break the law. He is simply arguing that he has a good reason for having done so, and therefore should be excused from all criminal liability.
In criminal trials, the most common affirmative defenses include self-defense, defense of others and insanity. Duress, entrapment and involuntary intoxication are used less often.
To see how one of these defenses works, let's look at the pending Trayvon Martin trial. George Zimmerman will undoubtedly argue that he acted in self-defense as defined by Florida's "Stand Your Ground" law. There's absolutely no question that he killed Martin.
If he can successfully prove he acted in self-defense, the law says he cannot be convicted of murder. He will go free.
http://blogs.findlaw.com/blotter/201...e-defense.html