The thing I don't understand from the people whom advocate that buying and selling used video games is wrong, is why they don't seem to feel the same why about other products. You can certainly make the same arguments for just about any product in existence.
The fundamental fact is that a copyright holder is legally able to produce as many or as few copies of their work as they wish and sell those copies under any terms they wish. But once a copy has been sold they relinquish all rights to said copy, unless otherwise agreed upon contractually. Copyright holders already have legal protections from people making additional copies of their work, that argument is a red herring when discussing used game sales.