An open-minded place like this isn't the place to find opposition to copyleft. One of the things that copyleft adds to the biz world is a sense of accountability: when people can choose whether or not to pay you, you'd better do your darnedest to be liked by them.
I think the Russian emulation site Emu-Land offers the clearest picture of how important access to creative works is to inspiration. Just looking at the American side presents a blurry picture of how we got from Venture to Diablo 3, but taking the Japanese side into account, the evolution of game design becomes crystal clear. Actually, most games today are variations on the original designs from the 70s. Football, for example, is very much the same game it was back then. The stories have also evolved in a manner that recreates the unremembered road from the beginning of conscious thought to the Epic of Gilgamesh.
Of course Diablo 3 is just Rogue with pretty graphics.