I'll never really understand the whole "X killed metal" or "X is ruining metal" thing. I feel like styles of music where there's a strong emphasis on an underground scene like metal, there's no one thing that can "kill it". If you know where to look for quality, you will always have quality. It's pretty easy in this day and age where there's a market for literally every style of music on the internet.
That being said, I think this whole Babymetal thing sucks and I honestly can't see this getting kids into metal. I think it's more likely for a kid to get into metal by watching that episode of SpongeBob with that Pantera song.
12/7 Bell Witch (?)
2/9 Black Sabbath