Bull crap. Explain why.
Training is everything.
The reason a US service pistol needs a decocker and be a double action,(or at least did) has to do with the nature of the troops. Your average combat support or service support soldier does not get a lot of time with the handgun. He had training in basic and if his unit TO&E has them he will qualify once a year......maybe. In-between the sexual harassment training and regular MOS stuff pistol craft does not get a lot of time. The only time you pick one up, at least in the guard is if you go to qualify or shoot in yearly TAG matches, regular training ain’t happening.
So for whatever reason a trooper is issued with one, three magazines and a M12 holster. It stays there on his belt, loaded with the de-cocker engaged. The only time it will come out of the holster is to clear the weapon or because the sh-t has hit the fan. There are two reasons for the double action; a surprise attack or when one is skulking under cover waiting for a target to get close enough for you to take a pot shot.
If one is pulling the gun out of a holster on the fly, the double action prevents accidental discharges. With the M9 you can pull a loaded pistol out of your M12 holster, using the trigger and it will not go off. Not so with the 6 lb Glock, where the safety is on the trigger. Every police department I know of has had issues with this and the Glock unless you have the NYC 12 pound trigger can go off if the shooter used the trigger to pull the pistol from the holster. It happens and some of the fancy combat holsters do neot make it any better. By the way these police are folks that use pistols all the time, army pogues do not.
Every army that issues the Glock has it troops carry it with an unloaded chamber. Sounds good except you need both hands to make the weapon ready, not the best idea.
Now the M9 is actually a good pistol (I am old enough to have trained on both the M9 and the M1911A1), as it has a loaded chamber indicator. So if you are in the dark you can tell it is loaded, flick up the de-cocker with one hand and be ready to go. Very quiet.
The M9 is very accurate, with M882 ball it is supposed to be able to put 10 shots in 3 inches at 50 yards when new. way better than the Glock or M1911 as issued. I know fellows that won their distinguished badge with an issue M9 (though selected ones)
It is big, it has the defect of the open frame but after 30 years it has done quite fine.