Now, think about the fact that it only takes a .22 pistol to kill the person carrying the M16.
With a reasonably good shot (often hard to do in the excitement of the moment). Better to have good stopping power than to be defenseless.
Take the case of the shootout in Wilmington, Ohio, February 17, 1997. Police and fanatics were blazing away at each other. The incident is most notable for being (mostly) caught on videotape (you might be able to catch it, if you didn't see it the first time, on Cops reruns.) Nobody even got hit despite apparently emptying their weapons at each other in a shootout where everyone is within 10-15 feet of each other, and at least two (the officers involved) presumably being somewhat trained in the use of weapons.
Later, one of the perps were seen in a parking lot and another shootout occurred. 26 rifle casings from the extremist's weapon were recovered there. The only injury was an arm injury to a bystander.
You can probably point to counter-examples, but I think you're exaggerating the "being able to take weapon away" aspect of the entire thing.
Nevertheless, I agree that the military have no business doing police work *whatever* weapons they are carrying. Police investigation and confrontation has an entirely different goal from the proper use of the military. It's an oversimplification, but a police officer is there to arrest criminals, and protect innocent bystanders, and a private in the army is there to kill the enemies of the United States and break enough things to persuade to not shoot back.
Trying to have one do the job of the other impairs their ability to do their primary job. Military effectiveness is decreased by "police actions", while police effectiveness is decreased by a "Shoot first and ask questions later" attitude - and when a police officer kills an innocent bystander, or even an unarmed not-so innocent or surrendering criminal, investigations, lawsuits, and even dismissals ensue.
If the U.N. or the U.S. wants to have an "international police force" of some sort, fine - train one that's designed to do that, don't coopt member nations' armies into jobs they're poorly equipped and not trained to do. If the U.N. or the U.S. feels it wants to go to war, then do so, don't go about it half-baked.