I think, in most situations, just seeing the intended victim with a firearm is going to be enough to sendan intruder running the other way. He's not going to care what caliber it is.
That said, if the intruder feels he has no escape and decides to fight, you're in for a tough ride. A .22 most certainly can be lethal, and, getting back to your stated reservations to do that, that's the only way a .22 is going to be effective. If the intruder has already decided it's a fight, the .22 in anything less than a head shot, is not going to stop the intruder.
First things first, get your mindset right. If you're not prepared to take a life to protect yourself and family, leave the gun in a locked cabinet. None of us want to take another persons life. But, I made up my mind a long time ago that if it should ever come down to me, or my family, over an attacker... I will not hesitate to use whatever force I need to stop the threat.