I believe the reasons below are the main ones people use when promoting used game sales (tell me if I missed some, this was done with brief thought):
1) People who buy used games for cheaper prices wouldn't buy it for the full price (not the best point as it doesn't always work)
2) By selling their old games they don't play anymore, people use that money to afford more new games (not as easily countered as it holds more weight)
3) It is part of basic consumer rights to be able to sell something they own (This reason alone makes it mind-boggling to understand why many video game consumers want their basic rights thrown away)
To be honest this sort of topic reminds me a lot of Star Wars Episode 3 --> Padme: "So this is how democracy ends... with thunderous applause."
