> losing your one child now?

You have likely not lived in a society where every family has many kids, so extended families have dozens of grandkids/cousins. It gets to the point that in times of plenty there's an "excess" and societies go to war in some sense just to see if they can carve out a bit of territory at the "mere" cost of some tens of percent of their youth. I mean.. why not? If you have half a dozen that "made it" and enough land for only two to inherit, flip the coin on the rest of them and maybe they'll find glory and conquer some new patch of land. Or not. What other option is there?

That's how people used to think and behave for millenia.

Modern life is very, very different to even just a couple of hundred years ago, let alone for most of human existence pre-history!

I read a statistic that before modern times something like 15%-60% of men died due to violence! For comparison, if you're an adult male in Ukraine, you've had about a 0.5% chance of death from violence, 30x to 120x safer in the middle of a war than during peacetime in pre-state tribal life.