But of course, thousands of years ago these kids would have been taught killing moves as young as possible so they could hunt/defend their village/etc.
Violence isn't ever going to be stamped out of humanity. By and large, it's less prevalent today than it's ever been. When was the last time your town was invaded, every man/boy killed, and every woman raped?
One could very easily argue that television and whatnot has helped reduce the violence. But in reality, they wouldn't be because anyone with an ounce of sense knows it's not even close to being the primary influence.