That's a peculiar definition of "sanity" (not that there's an objective way to define it anyway). Humans have been fighting wars since ever, just like other animals in herds. There's maybe an evolutionary advantage to it. Nations create armies to protect themselves and assert their territory (ok, nowadays it's interests). Since "sanity" is a socially defined construct, there's nothing wrong with the soldiers.
I think you have underestimated how much culture determine people's attitudes.
Consider a normal guy from my home country a few hundreds of years ago. He believed that he will only go to Heaven if he dies well in battle and is hence really scared of dying from disease. He wasn't a psychopath; he loved people and would die for his friends etc. He is normal for a clan society.
The same genes sit in me, which sincerely hopes never to have to maim or kill anyone in my life. Those human genes program us to be very programmable with the present culture. A powerful tool can often be misused.
The trick is to make the culture stay "nice". And to not have neighbours from clan cultures.
Humans have been fighting, yes. Fighting things humans understand, and for traditional human reasons, at their discretion.
What's new-ish (5-10k years) and completely against individual success, is a large and largely unwilling army driven to kill for reasons they don't understand or are lied to about.
If you are looking for a mass delusion we all participate in but understand little, look no further than the money in my pocket. OT, this article has some interesting insights on how organized states (and armies) actually led to less violence historically: http://edge.org/conversation/mc2011-history-violence-pinker
My problem with armies is that we have these essentially slave-cults for protection and we call ourselves free. Better off, sure. But not really free because we've got this slave system (Military justice/prisons) to enforce discipline in our enslaved warriors (they might have chosen to serve, but you can't reasonably give consent for personality breaking) without whom we're unsafe - or so goes the theory.
I simply feel that each and every one of us needs to tote a gun through mud, and know why we're willing to do it, to live in a society that practices war. Not only so that we choose wisely, but so that we're really safe - not just under guard.
