Unfortunately a .22 requires more than mere "good shooting." Shooting well enough to hit a dime sized target under the extreme stress of a life or death hostile encounter is well beyond the abilities of most folks. At least 98% of the "non-shooting" pro self defense community. These are the folks who will pick up a gun at a gun show or even worse from a gunshop on the advice of a salesman who knows how to sell, but not much about self defense and there's nobody competent hovering around like there might be at a gun show. Usually a salesman is telling the female he's selling to the cute little 22 (what attracts most girls is the CUTE factor if they're novices) is just fine for self defense. I have intervened politely many times in a sale because the weapon was IMHO inappropriate. At first the sales guy is indignant, but not after I help his client make a decision for a better firearm. Then they take their CCW classes from me.
For a person who dislikes recoil so much that they won't practice with a 22 or has some kind of physical infirmity that prohibits them from shooting a heavier caliber, just shooting a 22 "well" ain't gonna cut it. Anybody close enough to notice a solid hit from a 22LR is going to be able and I'll bet.... willing to kill the defender unless the first defensive shot results in a neural band "no twitch" shot. Such shots are imminently possible, police snipers do them all the time. So do MOSSAD agents and various and sundry other dirty trick dept alphabet soup agencies all over the world. It requires training, skill and....PRACTICE. More practice than most people are willing to give.
OTOH, which would you rather face as a bad guy in the 250-325 pound fat slob range....a little old lady with her Beretta JetFire 22LR or that same lady with her S&W 9mm Chief's Special or something even bigger? The behemoth bad guy isn't even going to feel a 22 in the gut...at least not right away. But he'll notice anything the size of a 9mm or bigger. He notice it a lot more if he's hit a lot more. Multiple 9mm shots in the area of the abdomen are far more likely to cause the cavitation needed for a more immediate incapacitation than multiple 22's. It's a matter of cross sectional density of the round. Or in other words....in this instance size matters!