I am a new shooter. The entire caliber war seems a little silly to me when one thinks about it. The goal in shooting from what I have gleamed is to put multiple shots on the center mass. Granted, if anyone had a choice, a M1A1 tank or even a JDAM strike would be prefered the prefered choice, but in a squeeze a pistol will do.
The goals I have for myself is shoot accurately, not to over penetrate and hit the neighbor, and show good judgement when to use lethal force. With those requirements in mind, the 9mm suits my purpose. For me, the 9mm is not to snappy for a novice like myself, relatively an inexpensive round, tons of different type of gun frames that it is chambered to, and is a dependable round.
Now the wife wanted .40's (she is 6'3" and not a wilting flower) because she has had experience in firearms (Dad was a 20+ Chief Petty Officer in the Navy). I explained to her that I have shot .40 in the past and had problem dealing with the recoil and control (yeah, I am a limp wristed sissy, live with it), and I really had very little experience (.22 rifle at summer camp and shot a friend .40 Glock once). She is now happy with another 9mm gun whose name shall said on this forum ((cough) Ruger) because she is left handed.
I do not think .40 is anymore deadlier than 9mm. Both will ruin your day if you are hit by one. Both are dependable rounds for pistol (Or else we all have .22 and be driving better cars because the cost of ammo). Both have a fan base behind it.
As for LE and FBI, economics and politics will always have influence. I still think the old Model 10 .38 specials are good gun for rural LE and that ammo capacity dose not make the job safer. Training and knowing what your are walking make the difference. If size was the soul factor, the local sheriff would be zipping around in a Bradley and look like he came off the street of a Iraq city.
In the end, the .40 is not going away though I think it is a redundant compromised round between the 9mm and .45. It is all up to shooter.