The 22 lacks the power to immediately stop an attack. If you use a 22 for defense, you run the risk of getting shot before the threat has been eliminated.
Getting shot, or stabbed, or clubbed or whatever ..... you want it to stop RIGHT NOW!
Rules of Self Defense:
1. Pay attention, and you'll avoid having to use any weapon in all likelyhood.
2. Have a GUN. No sane, rational person wants to be shot with anything. Pepper spray "foggers" work both ways indoors or if the wind is blowing, and really determined people will not be deterred by stinging eyes and burning lungs. Even the most wacked out crankhead on PCP will stop beating you after a minute or so of no respiration.
3. Have the best gun you can in the situation, and be as proficient with as you can be. Bigger holes are better than smaller, more (energy/penetration/#of holes) is better than less, and only hits count.