It would not be my first choice.....
But it's certainly on my list. IF I were in "gravest extreme", and had a .22 in reach, I would certainly not pass it up thinking "oh crap, its only a .22 and won't work".
The .22LR is our premier small game and practice round. And it certainly will kill people. You can look in the "Armed Citizen" column of the American Riflman, and see numerous clippings every month where a .22 drove off an atttacker, and sometimes mulitple ones.
The purpose of a defensive firearm is to defend yourself. How that is done (and with what) is not as important as the fact that it gets done.
The
ideal defensive handgun is one that is powerful enough to be relied on to stop a fanatically determined attacker. And the .22 is not. It has done it, and will do it again, many times. But it cannot be relied on, with confidence.
The majority of the time, the mere presence of a gun deters criminals. Many times criminals who get shot (with anything) will flee if they are physically able. To me, those are successful defenses.
But we plan for the worst possible case. And that is the fanatic (for what ever reason) that will not stop until physically incapacitated. Make no mistake, a .22 is deadly force, but may not stop someone, until it kills them. And sometimes, that's what it takes, even with the biggest, most powerful rounds.
Another of the problems with the .22 as a defensive round is that it is cheap. And because it is cheap, people tend to buy the cheapest .22s. And the cheapest .22 ammo is not nearly as reliable as a centerfiire. Misfires are not uncommon. With hi quality .22s, they still happen, but are much less common. Feeding in semi auto pistols is not 100% reliable, each gun being a law unto itself about what (if anything) it will feed reliably.
The .22 makes the list of homicide calibers, because a lot of people have been killed by a .22. But murder is quite different from stopping an attacker.
If a .22 is all you have, or all you can manage, you are still far from defenseless. I knew a state trooper many years ago who's home defense gun was a Ruger Mk I target model. He could dump the full mag so fast it sounded almost like a single shot, and cut the eyes out of a standard Sillhouette target at 15 feet faster than you can read this sentence.
I'm not that good, so I rely on larger calibers...