I would personally not recommend anything less than a 9mm and would prefer larger. 32, 25 and 22 are just a joke when it comes to SD. Yeah, yeah, I know they will kill someone, but that's not the point. A SD weapon is meant to stop an aggressor before they can do damage to you and those calibers are truly bad at doing that.
Bear44, I respect your opinion, but you are so far away from what really matters on this, it is hilarious. OF COURSE, the point is to kill the aggressor, what other point is there. I do not believe that we will get the opportunity to choose whether we can kill the aggressor before they do damage or kill the aggressor after damage is done. Since the guns you dislike will kill the aggressor, they have to be defined as SD guns, whether you like them or not. You did not present any facts to back up your statement, just your opinion. Like I said, I can respect your opinion, but I take it as just that, your opinion. I don't agree. A carried gun is a SD gun. A gun left at home, is worthless regardless of the caliber.