+1 Theohazard. In addition...
Choosing a self-defense or home-defense weapon is all about compromise. A .22LR handgun IMHO does not measure up to a 9mm or .45ACP handgun, but then again, none of the above will measure up to a 12ga shotgun, a .44Mag lever rifle, or a .223/5.56 carbine. However, a .22LR pistol is far better than nothing at all.
Gun forums are rife with attempts to conjure up some sort of "magic factor" to equalize broadly differing firearms. Many of these discussions begin to border on the absurd if they continue long enough.
There is no magic equalizing factor. The question is what compromises YOU are willing to accept.
That being said...
IMHO the main advantage of .22LR for SD is that it will fit into extremely small pocket-sized "mouse guns" like the Beretta 21 or Taurus PT-22. However, as the gun gets larger, .22LR pistols are at a capacity disadvantage because it is inherently difficult to stack rimmed .22LR cartridges in a magazine that will fit inside a pistol grip. Consequently, as the gun approaches even so-called "compact" size, you'll encounter numerous 9mm models that hold 12-14rds- more than virtually any .22LR pistol on the market. At this point, there is little reason to choose .22LR unless the shooter is
very recoil-sensitive and/or has an extremely limited ammo budget.