I am one who considers "defensive handgun cartridges" to be under powered. For me "defensive handgun cartridges" include (but are not limited to) .38 special, 9mm para, .357 magnum, .40 S&W, 10mm auto, .44 special, .41 magnum (moderate loads), .44 magnum (moderate loads), .45 ACP, & .45 Long Colt. They are under powered which is why we are trained to shoot twice (or more depending on the cartridge and training), assess, and proceed as necessary.
It is not an issue of lethality. It is an issue of incapacitation. An issue of stopping a threat as quickly as possible with a compromise weapon and cartridge. A handgun is a compromise that is "good enough" in the mind of the user. It is what that user will likely carry and have at hand; rather than something bigger, heavier, more powerful, and more effective that the user would not chose to carry or find impossible to conceal.
Not all handguns are under powered. Nor are the ones I listed weak, in my opinion.
NRA Life Member - Orange Gunsite Member - NRA Certified Pistol Instructor
"When plunder becomes a way of life for a group of men living together in society,
they create for themselves in the course of time a legal system that authorizes it and a moral code that justifies it." Frederic Bastiat