Not the concept of selling games, hey its your game do what you want with it, I MEAN YOUR PERSONAL GAMES.
I can honestly say that I have never sold or traded away any of my games in the 21+ years I've been playing them (losing them cause you can't find it doesn't count ;p). Sure I've bought bad/disappointing games like Rogue Squadron III, Red Steel, and Metroid Other: M every once in a while but I never sell them. In my mind it's to remind me why such a game is bad by actually playing it, plus the memories, no matter how horrible, have a lot more weight when you still got the dam thing.