I consider the 22LR to be a viable SD cartridge in the proper firearm using good quality proven ammo. It is an experts SD cartridge and must be used resolutely and with precision.
One good example of a suitable SD 22 pistol would be the Beretta Model 70, which has combat history with the Mossad.
Another might be the Ruger SR22. It is combat configured with good sights and a decent trigger...Mine has proven 100% reliable and very accurate. Loaded with MiniMag solids, in the hands of a person who has spent hours shooting thousands of rounds...let's just say I wouldn't want to face that regardless of what more conventional SD caliber pistol was in my hand.
Still waiting for my Flashback...I would like it now, please.