I don't want to repeat what has already been said here R/E the suitability of the .22 lr for self defense. What I will say, that is not mentioned often enoiugh, is training. Way to many people carry without the training and confidence to back it up. Most of us on web sites like this are shooters, so it's hard for us to understand that the average person carrying a gun is often times in over their head when it comes to when and how to use their weapon.
Practice makes perfect, builds confidence. If in a life threatening situation, you have to think and commit quick to what ever action you are going to take. Hesitiation, indecision, lack of basic shooting skills will get that weapon taken away from you, and shoved where the sun don't shine, if you are lucky.
I guess what I am trying to say is practice leads to skill and confidence, and it's very important. A man, or woman, who knows what they are doing, and are comfortable and experienced with their .22 is a lot more deadly then someone carrying a 40 s&w who goes to the range once or twice a year, and fires half a box of ammo.
Larry