I'm assuming that 50 there is a typo; most second-hand games i've seen in stores are about 10% cheaper, which for me has always been the reason not to buy them (for only 10% more i have a shiny new one).
Apart from that, I think the vast majority of the money received by people selling their old games goes straight into new ones, so if the publishers 'defeat' second-hand sale, people who usually sell their games won't have as much to spend on new ones. People who usually buy used games might buy a few more new ones now, but less than they would second-hand. So the only thing the publishers are really taking here is second-hand markup by stores. And while that is quite a bit of money, I'm not convinced that that amount is worth screwing your real customers over.
But then again, service to customers has been lost down the drain of shareholders for quite some time now. As customers, we're the meat being sold, not the other way around.