I don't think it can be understated how much of a fatal blow to many people's gaming habits the absence of a viable used market will be. This is not just about Gamestop. Look at the broader picture. Think about the millions of people who buy used games from people on craiglist every month, and the sellers who sell their stuff on craigslist to clear out space and make a little extra money. Think about the millions of mom-and-pop vendors on Amazon and eBay who make a living (or at least a nice supplemental income) by selling old merchandise including games, movies, and books. Think about a college kid selling a couple games he's done with to a friend for textbook money. Think about the number of family members that give away their consoles and games to other families or their kids for presents. Think about donating video games and consoles to charities (including Child's Play) and the kids who start their gaming thanks to that.
Just consider the sheer number of people that are only able to participate in gaming because of the price discrimination offered by a healthy and non-fixed used marketplace. These aren't the hardcore day-1 $60 purchasers that need AAA gaming, but the more modest parents and families who buy a bundle of used games and a console as a cost-effective way of entertaining the children for months on end, or the college students who just want a few games for their dorm room. Killing used games means these people won't be able to buy into video gaming at all without spending more than they would be inclined to, and essentially locks them out of the market because they can't afford, or don't want to pay, full MSRP for every single thing.
Video game consoles are a luxury good, I won't deny that. So if MS really wants to position themselves as a super-premium device just for the gamers who are so hardcore that they pay full price for every game and never need to sell anything for cash, that's their call. But even within the space of a luxury good, used goods and lower price points help expand the userbase well beyond high-income early adopters (especially years into a system's lifecycle after its price drops considerably), and ultimately bring in many more people to the hobby which is good for the industry's ecosystem overall, because those people still buy new games as well. The PS2 was massively successful not on the backs of hardcore gamers, but on the backs of the large amounts of families that were able to build up large libraries of mid-priced titles after the system price had dropped.
MS is making a very large bet that essentially those people don't matter. They're betting that the lost revenue from all of those people not being able to participate in the marketplace at all will be more than compensated by even more hardcore day-1 $60 purchasers and more DLC and skins and digital crap. They're betting that their hardcore crowd will be so locked in to the Xbox ecosystem that they'll not only buy as many games as they did before, but they'll spend even more money within the system to do so. They're narrowing their focus exclusively to the super-hardcore enthusiasts and early adopters with high disposable income, and shutting out everyone who isn't. They're not just marketing their system as a high-end device, they're explicitly saying "If you can't afford the cost of full-MSRP games on this platform, don't bother. If you could only afford to buy our games by selling off old ones, you're not invited."
Rather than expanding the market, they're deliberately contracting to an even smaller segment under the ridiculously naive theory that all those hardcore fans will more than make up for smaller userbase, and the revenue that would have gone to used games will now go directly to them. But of course, it won't. If people can't afford to buy games at the price point they desire, they'll just buy something else. Given the increasingly significant threats to console gaming not just from mobile and tablets, but from YouTube, Netflix, Hulu, Facebook, and the thousands of other services out there all competing for our free time (which is increasingly becoming as much of a scarce commodity as money), consumers can afford to be as picky as possible in much they want to pay for disposable entertainment.
It's an arrogant, exclusionary, elitist, and short-sighted move by a corporation more interested in nickel-and-diming consumers than creating a healthy, vibrant long-term industry, and it deserves to fail.