If you choose to own a gun for protection, you have a moral and legal responsibility to get proper training. That training should cover when lethal force is justified, and what happens after a shooting, including the psychological and legal consequences. The NRA Personal Protection courses address just these issues. There are many other good sources for this training also (LFI, etc.), but the NRA courses are a good (and relatively inexpensive) place to start.
If any of us uses lethal force, the legal system will investigate, and that investigation report will likely include any online or e-mail statements we've made about the use of lethal force. So when you post, imagine the prosecuting attorney reading your posting to the jury, because that's what will happen.
Lethal force rules vary widely. Imagine an old lady in a wheelchair who gets tired of being repeatedly robbed, so she sits up with her shotgun waiting for the robbers to break in again. They do, and she kills one. In Texas, they'd probably give her a community service award. In Massachusetts, they'd probably imprison her for first degree murder.
I was taught a rule that works everywhere, including Massachusetts.
Lethal force is justified only when there is an imminent and unavoidable danger of death or grave bodily harm to the innocent. Imminent means you have to wait if you can. Unavoidable means you can't get away, and you couldn't have avoided getting into the situation. If you can't avoid the threat, and you can't safely wait, then you shoot to stop the threat. Once the threat is no longer imminent and unavoidable, you stop shooting.
So warning shots are never justified. They also place the community at risk, since your warning shot could hit someone. Leave them for Hollywood and naval gunfire.
I think a legal system that says essentially you should be killing people instead of "warning" them is pretty screwed up.
The legal system is certainly a mess, but it is also the reality we face. You need to understand the system that will judge your actions, so you can plan your actions accordingly, and train yourself accordingly.
Please, no warning shots. Warning shots are a construct of hollywood and the Coast Guard.
Having competed with and trained with the Coast Guard Academy's Combat Arms folks, I would advise treating them with respect. They make good use of their large training budgets, and they're very good.
At sea, a shot across the bow is a clear form of communication. Ashore, a warning shot is usually illegal and almost always an irresponsible act.
Quite frankly I think if I was in a situation where somebody was in my house and threatening me with a knife or a gun - I would rather (perfect world scenario) blow his kneecaps off and see him in a wheel chair for the rest of his life than see him dead. I would rather see somebody pay dearly for being an a**h*** than let them off the easy way. But that's just me, I'm sort of vindictive like that.
A person without kneecaps can still kill you. You should only shoot to stop the threat. It's not your job to punish. Your job is to protect yourself and your family.
Once he goes down I end my defense, I don't kick a person in the balls when they aren't a threat. But while they are standing I won't back off.
Most people shoot better from the prone position. Just because they're horizontal doesn't mean they're no longer a threat.