Basically everyone wants to get in on the used game market so they can rip you of too. Gamestop fucks you over by giving you almost nothing for your used games, then sells them for $3-5 less than a new copy. That gives a much larger profit margin than a new game. I don't buy used games from Gamestop, and I won't buy them from Best Buy either.
If I want used games, or to sell my games, I'll buy/trade with people, not with some store that won't give me a reasonable deal.
And no, I don't think there's something wrong with used games. If I can buy a used DVD, book, whatever, why not a used game?