Kinetic energy is the force to move one pound one inch. That means moving a hand, about a pound, maybe two, plus gun around 200 to 300 inches. While some is absorbed, not by porting though, that only imparts muzzle blast. 500 pounds is not absorbed, and is not imparted to the hand, plus it is a well known fact that even with a vest to spread the energy out instead of penetrating there is not as much force as a punch from a boxer.
I don't think anybody needs to justify the purchase, or owning a gun, but I refuse to drink the kool aid myself. I know for a fact that at least one homicide was committed with a 22 short, and it was a immediate stop. Had nothing to do with exaggerated kinetic energy, it had to do with a hole in the brain that the brain did not come with.
Excluding muzzle blast the energy a bullet has it also puts the same energy back to the hand. Which if shot in the hand it would not be a game stopper, even if it was a 500 S&W, the person could still attack with the other hand. I applaud him, congratulate him on his choice of round, but it is not the holy grail, there is no such thing.
With smaller calibers I tend to push them hard, with heavy calibers I download them. I rely solely on shot placement for doing the job. And when I compare the 40 to the 10 with the exact same bullet, exact same gun, exact same velocity only difference is case length IMO the 40 out performs the 10. It is more economical, uses less powder, I can buy once fired cases for 5 dollars a pound, far cheaper than 10mm. And most important there will be less muzzle blast from the 40 compared to the 10, making my chances of shot placement higher with the same amount of practice.