It happens every time, if there a way to make money speculators will come into the market, take advantage of it. Or in the case of index funds, it will become overcrowded and inefficient and the market will move on to the next big thing. Just ask LTCM. It's the invisible hand of the market...
Honestly, anybody that down voted me is probably invested heavily in index funds because they heard something on a blog and listened to Warren Buffet once.
It always happens...