OK, show of hands: Who WANTS to get shot with a .22?
Umm... not me. But then again, I don't want to get shot with a pellet gun, a sim round, a paintball, or even a rubber band. That doesn't mean that any of those are going to incapacitate me if I get shot with one though. (Though in all fairness, possibly with the exception of a very well placed .22)
Honestly, if you were protecting your family from a home invasion or a car jacking or [insert SD shooting here] would getting hit by a .22 (even a hit uhh, below the belt) really make you put down your guns and say "I'm hit, please don't hurt me!"? Then you have to think about any chemical substances your adversary might be on (as well as adrenalin, which is pretty potent in and of itself) and your adversary might not even feel the hits if they're in non-vital areas. There have been many cases of people being injured or wounded in fights and not realizing it until well after the hostilities had ceased.
I seem to remember a story I heard here a few years ago where a man was assaulting a police officer and continued to fight even after taking 6 rounds of .45 hydrashoks POINT BLANK in the torso until the 7th (and last) shot to his CNS finally stopped him. The point is that you can't always count on even a well respected service caliber to stop someone immediately, much less a round that the majority of people relegate to target practice and pest control.
While a .22 definitely beats a pointy stick, I think it is irresponsible to use the cliche of "well I wouldn't want to be hit with ___" to insinuate that a .22 is as good of a man stopper as a service caliber.
Ariel: A .22 is better than nothing, and is a great place to start and learn the fundamentals of shooting, but definitely don't mistake it for the be all, end all of defensive firearms.