The article is wrong about needing the largest caliber pistol to stop an assialant... Serious studies of real shootings have show that an accurate shot with a lower caliber is just as likely to take down the bad guy. And - as the author pointed out with shotguns - a 20 ga. shotgun would be better handled of many people (smaller stature, less strong, etc.) and yet not lose much knock down at relatively close range versus a 12 ga....
The best defense caliber is one that does not cause the shooter to close their eyes, flinch or hesitate... Few people are accurate shooters in a sudden unexpected terrifying situation - adrenaling pumping, frightened, etc. So having many smaller caliber rounds - means in case of 9mm up to 14 rounds in a Browning HighPower... vs about 1/2 in a powerful .45 ir 357. I think any gun that hits where it is pointed by an average person because the recoil did not knock his/her arm and head back is the best most reliable defense. There is power in numbers... Note: .22 cal. killed Robert Kennedy and nearly killed Reagan ...
.22 LR is the preferred round for assassins, spies, hitmen, etc.