Free: Contests & Raffles.
The biggest downside to a .22 for defense is that the ammo is more likely to result in a dud than centerfire ammo. May not be an issue with a revolver but a semi auto could quickly become just a blunt object to hit with. The little Beretta Bobcat is a great carry gun but it would require a pocket knife to clear a dud.
Assuming we are looking to protect ourselves from two legged threats? If you put a .22 round in the kill zone the target will die, at least eventually. The problem is that a .22 is lacking a bit in the power punch knock down zone. The threat may just keep coming at you before they expire. I would definitely opt for something larger if at all possible.