I own over 100+ retail 360 game, i've been a member of xbl since the xbox days, I even owned more than those 100+ retail games, because I resold about 20 of them on ebay at one point to fund for something else. I've owned over5 xboxes 360 over the years since launch due to the various hardware problems of the first unit; and bla bla bla. I never buy used games, but I live in a rather poor area, and whenever I visit a gaming shop, i see tons of kids raiding the cheap used bins. For kids, used games are an incredible deal.
Preventing this is just.. shitty. It's not cool for gamers, for families and for the kids who cant afford new titles all the time but just want something to play to waste some time. I expect a massive backfire from mainstream, average joes. Parents will simply go for another console if the games are cheaper and if they can play those cheap used copies. I hope that Microsoft is not forgetting about the giant monster that is Apple and Android powered devices. The Initial cost of the device can be expensive, but I am expecting that parents will simply move to them. Those 1.99$ purchases keep the kids busy just well enough.
I honestly hope that Microsoft will reconsider this decision. Even if it's not a problem for me, I will not consider it as a viable purchase, even if I never buy used games myself. If Sony pulls this stunt to, I will simply move back to PC gaming.
It's just a terrible business practice; and since I am into collecting, this no second-hand policy will kill the collecting marketing eventually.