I think people believe that a .45 ACP or .357 mag = one shot stop. Period.
Most think that if they go to the range a few times a year and can hit a pie plate at 7 yards consistently with one of those calibers they are good to go. I'm not talking shooting from holster, I'm talking about picking the gun up from the bench.
I prefer to carry my XD .45 because I've shot a few thousand rounds through it and am fast and accurate out to fifteen yards with it. I can slow down and get nice hits with it out to 25 yards also. I will not hesitate to walk outside with only my Bersa .380 because I've shot about 800 rounds through it and am also fast and accurate with it. I have also practiced malfunction clearing, speed reloads, one hand firing (dominant and non-dominant) and so forth with both weapons.
As soon as I get that kind of round count through my M&P 9mm it will probably see more holster time as it heats up.
The most important consideration of a carry weapon to me is how it fits my hand and how many rounds I have put through it to know I trust it to perform and that I am familiar enough with it that I can operate it (load, reload, clear a stove pipe, manipulate safeties et al.) and shoot it quickly and accurately without consciously thinking about it.
I personally would not carry a .22 but if someone has trained with it and can hit 3 shots to the chest with it quickly and accurately more power to them. Better to have a gun you can shoot than to trust the mythical one shot stop power of a handgun that you likely could not get a SOLID chest shot with at 10-15 feet. I know that I would probably be a better shooter today had I started with a .22 and moved up instead of having to break myself from the flinching I picked up from my .40 cal.