I will say that if games are not available any other way, then sometimes it becomes necessary to acquire less-than-original copies. What I am talking about here are out-of-print games, defunct games, etc. I am not talking about current market, new games available.
As for used games, developers don't like them being sold because they don't get a cut (authors don't get money for used books, musicians don't get money for used music, why game developers feel they should be different I don't know). But they don't realize that people often sell used to buy new -- or buy with the thought of selling after they are done. Why else would there be so many copies of popular games available new (e.g., GTA IV).
I freely admit buying used games. It is cheaper, usually with little (if any) loss of quality -- if you buy ones in good condition (sometimes, I will admit the condition is so good you wonder where they came from). I also buy used because sometimes you want to try-before-you-buy (permanently) -- and that option is available with used (at least form Gamestop).
Mike from Morgantown