It's one thing to say "no warning shot for me, I'd just blow the sucker away", and another to actually be there and take a life. It just appeared to me that the guy was in a position where he didn't want to take a life but knew if he didn't warn the lunatic forcefully and immediately, he would imminently be in a position where he would have to kill him. I can agree and say that warning shots are a bad idea for all the reasons given, but I can't bring myself to say that this guy necessarily did the wrong thing in this instance.
Putting aside the crazy dude's return with a rifle (couldn't have predicted that), would he have been better to have just shot him?
Here's a hypothetical example of my point: let's say you're sitting on your front porch unable to get up quickly but happen to have a gun handy. A relative that you care about shows up, and for some reason he's completely out of his gourd. He charges across the yard swinging a samurai sword at you. You have about four seconds before your life is in serious danger and the only thing you have time to do is either shoot him dead or fire the first one into the lawn in hopes that the loud bang will put some fear into a crazed mind and stop the attack.
All legal issues aside, your only concerns in that moment are for your own life and that of this crazed relative that you still care about. Assuming you have a couple seconds for a safe warning shot, do you give that a try or just blow him away?
Again, I'm not saying warning shots are a good idea legally, but in certain specific circumstances I just can't condemn it.
..... What if your gun jams?
I think the most common issues usually had with semi autos is magazine related, either dirty, or not seated enough, etc. You are only really garenteed the one in the chamber.
I have tried a warning shot with a bear, and it didn't deflect it from its path.