One documentary on Japan after WWII illustrated this best. After the war there were tens of thousands of orphans running around in Japan. The girls were al sold up as sex slaves and the best looking ones sold as brides. The boys, however, were all simply KILLED.
They'd wander around in the ruins of buildings and every week there's be fewer of them. Who killed them and what happened to their remains is a complete mystery. They were simply killed because they weren't useful in a society that needed labor and couldn't afford to have more mouths to feed.
I believed Japan to be a civilized society but the above story has made me change my mind. If you go around killing children simply because they're not useful you don't really deserve to exist as a society.