The women with enough integrity to not have offspring with the invaders who just killed their tribe didn't survive. The men were killed off at exponentially higher, rates with only the ones who didn't die in battle that day surviving. And the ones who become slaves had a fate worse than death. Roman's would justify slavery by stating if they were in that position they would die before becoming a slave.

Also, the men with "enough sympathy to spare the next generation the burden of existence" didn't reproduce either.

Children used to be a necessity for survival to increase production. Now, children are a trophy for the parent or an unwanted accident. You'd never find accurate statistics on this because very few will admit their child was an accident forced upon them by a spouse.

And while we're on this topic, ALL PARENTS are technically murderers. Of their own children.