A large chunk of modern military training is explicitly to prevent guys from saying that reflexively.

It actually has toned down some, if you can believe it (at least in the Marine Corps).

I guess it had to happen, given the "police actions" undertaken these days.

it's always been like that, step one is to de-humanise your enemy so your soldiers do not feel guilty for killing them.

The problem is that in some wars, if you don't, the enemy will strike you just as hard or harder.

You have just described the philosophy behind the fire bombing of cities, nuclear escalation, and mutually assured destruction - which given Vonnegut's Slaughterhouse Five was surely what he was talking about when he made that comment.

Fortunately the political leaders on both sides knew that they could never use nuclear weapons. Reagan was horrified and changed his policies, much to his credit, when he realised that the Soviets really were terrified of an attack from the West.

Even Khrushchev, who had a lot of blood on his hands, couldn't sleep for days after he had been briefed on what a nuclear war would actually mean - he only calmed down once he realised that the things would never be used by either side.

You're missing a 'probably' in there somewhere.

I think it's just my retrospective naive optimism!

The "guys" in the above sentence include your enemies.

Surely a self-fulfilling prophecy.

That is why I shoot their women and babies.