Well, it's two things really. First, most of the console crowd is somehow under the impression that they own all of the software on a disc when they purchase a game (and therefore the right to resell and distribute it). The licensing practices that have been a part of the software industry since its inception escape most console gamers, so they fuss when companys start exercising the legal disclaimers that precede every title screen.
Second, the ability to resell/distribute games is a major perk of consoles. When you eliminate that from the equation you create a lot of problems: people can no longer share games with friends, you can no longer buy at wholesale, rentals become complicated, and so on. More importantly, when your console bricks you get hit with a one-two punch if you have a large library. In essence, it's a big issue because restricting used games eliminates most of the advantages of console gaming. It creates red tape and door charges where currently there aren't any.