That's complete and utter nonsense. Any person trained to use firearms will tell you that when you shoot someone you are shooting to kill. You're probably referring to a myth around a very specific type of bullet:

No U.S. military service rifle caliber has been more controversial than the 5.56x45mm cartridge. Since it's adoption in the 1960's, Soldiers and civilians have both circulated the myth that the 5.56 round was designed to wound the enemy and not kill them. The logic behind this claim is that wounding the enemy puts a strain on their logistical systems with the added bonus that it requires other enemy soldiers to carry off their wounded brethren thus lessening the number of combatants on the field of battle.

The only problem with this myth is that it is just that, a myth.

The U.S. military has never published any documents, requirements or doctrines stating a desire to adopt a rifle cartridge designed to only wound the enemy. Of course the military views wounding as better than no hit at all, and taking an enemy combatant out of the fight they view as a good thing. But they have never built a doctrine around the concept of wounding being the desired result of a gunshot wound.

The 5.56mm cartridge was designed to kill not wound or maim.

So you're talking about a myth that applied only to a single type of bullet and applying it to all bullets.