Something I just picked up on
Chris executes Barnes in almost the exact same way that Barnes executes that wounded Vietnamese soldiers after the first fight, stands over him for a couple of seconds before shooting him 3 times in the chest.
My take is that it's saying that Barnes has become just as bad as the enemy and that Chris has become just as ruthless as Barnes is.
"I really wish Gia and Claire had became Tanner" - Honeybeefine