Technically yes they can be "beaten" that way but I personally prefer to kill as few people as possible. This is part of why I don't want to get too into hardcore combat stuff here because I don't want people taking it then going around acting as judge, jury, and executioner.

Your average footsoldier is not the enemy. He's not he one making the decisions of who goes and fights where and what. He either does what he's told or suffers for it and probably doesn't really know what's going on in the first place. They don't deserve to die for that. In all the stuff going on these days I bet there's maybe two dozen people at most who really are hardcore megalomaniacs who would rather destroy the world than lose their grip on it. Those are the people you cannot use diplomacy on. Everyone else is just a peon to them.

You don't need to kill someone to win a fight, you just need to remove their means or desire of fighting. I would much rather disarm a footsoldier than kill them. Its not that I'm a nice guy or anything, just that he's not the enemy. And now if he gets given another gun and told he has to go out and fight again for the same reasons he might be a bit more reluctant and shaken when he remembers what happened last time. Especially if he feels that the only reason he's still alive is because his enemy spared him las time. Instill that doubt in enough footsoldiers and eventually you'll create a schism in the ranks. It also helps when you clearly inform them of what your intentions are and why you didn't kill them.

Its also a LOT harder to hit a gun than a whole person whether in melee or ranged combat so you'd better be really accurate. If you're not you will be after awhile.

All wars are psychological in the end. You don't try to wipe out the other side, you try to make them give up. I guess the exception would be a zombie apocalypse where you really do need to just kill them all before they kill you.