one of the important points to my mind is that in this sort of defensive situation, as well as in hunting, a second shot is not always going to be possible. Imagine if you will, a dog, large or small, coming at you rapidly, and you have maybe a second to decide. you have maybe one more second to draw and get ready to fire. At that point, charging bear, charging dog, cat, so forth, it may already be on top of you. You may have only one shot, and you can count on the fact that after your free shot, the animal will be engaging in high speed evasive maneuvers, hit or miss.
So, if the banger down the street has a really antisocial rottweiler that he has let out, and it's bearing down on you, I suggest that a 22, and the single round that you may be able to get into thethings body, is just not going to do it.
If you're someone who can pop out a 22 pistol and empty a magazine into a moving target in a few seconds, then yes, a .22 is good enough. Otherwise, you need something that is going to disable the thing with a single body shot.