This argument will go on and on until the end of time. What no one seems to understand is that when you are talking about 9mmvs 45vs 40, you are talking about a whole classof arms tha basically do the same job. There is no real difference in any of the "service "cartridges, because thet were designed to do the same job, under basically the same conditions. A nine millimeter full metal jacket, and a .45 full metal jacket, at a slower speed, will off very close to the same energy, and while momentum goes to the 45, if either of the cartridges would literally "knock down" a victim, it would also "knock down" the shooter.
All "service " calibers, from the .30 luger, 7.65 mausert, 7.62 Tokarov, to the 455 webley are basically the same in performance, althoght the Tok is a lot more deadly than people would think. It is only when you move up the scale to the 357 magnum from a long barrel, the 10mm loaded all out, and the 41 and 44 magnums that you get a real difference in killing power. The reason .44 magnums weren't issued to troops has a lot more to do with the cost of training someone to a high enough standard to hit anything, and the cost of a good quality revolver than anything else.
In NC, the basic pistol class in the Basic law enforcement curiculum requires four hundred shots. That's just about enough shooting to get really good and scared of a 44 magnum. It is a whole lot easier to train them to a level of skill that might save their life with a good, heavy frame 9mm than anything else. Also, have you looked at the price of a qualit DA revolver lately? Colt 1911 clones can be had fr $400. not so for a magnum revolver. The long and the short of it? Set very high standards for your personal marks man ship, and practice often. Shoot the biggest gun you can hit well with. Get the gun that "points " most naturally for you.
And don't sweat the small stuff. In places that are a lot more violent than here, such as Isreal and South Africa, people get by just fine with 9mm ball. It's hard to argue with two or three through the skull. same in S.A. 38 special solves a lot of disputes down there, and no one seems to complain. It has a lot more to do with shot placement than anything else.