Well, several people have pointed it out, already, but I have a small story.
Probably around 2006 or so, I was looking around in Gamestop, and decided to look at the used games. Now, I NEVER buy used games. I'd rather spend five dollars more and avoid any nasty business with the previous owner using his disc as a Frisbee before he sold it.
However, I found two games. Suikoden and Xenogears in the used game section. Now, I had played Suikoden 2 (one of the best games on the PS1) and was interested to play the first one for several reasons. I had heard good things. The sequel has several returning characters taking place just two years after the first one in a nation just north of the first one. And there were all sorts of bonuses if you loaded save data from the first game.
Xenogears was also tempting as I heard so many good things about the game.
The games weren't cheap at $30 and $50 a piece, but both also still had their instruction manuals. Still, I didn't buy them. I took some time to decide if they were worth it. A few weeks later, I did return to buy those games.
I never could have done that if the used market was crushed by DRM.
Plus, they are my games. I have so many problems with the idea that Microsoft can just say, "No, you can't play used copies." I was the one who bought the game. It is my game. I can do what I want to with it. And that includes using it as a Frisbee, if I want. It's my game after all.