Let me explain a little why I think DRM is bad. Let's suppose you have a computer, it runs a version of Windows. You purchased a game and played it a little, it had DRM, but for you it was almost as if it had nothing. Some years later you upgrade your machine and change to a different Windows. The new Windows has some security measures that prevent the old DRM from running. You still own a valid license of a game that's no longer usable in the old machine, because the old machine is broken. You have every right to install that game, but you can't. Because the old DRM does not work, and the company that made the game no longer supports it.
This could also happen if you changed your operating system to Linux and tried using Wine to run the game, or if you changed your computer to a Mac with OS X. The non documented tricks a DRM does to prevent unauthorized use just don't work well with emulations. A game that could have a broader gaming base just decided that it was better to cut a lot of machines from it.
Of course, this is if the DRM scheme lets you play the game in the first computer at all. A little Internet search shows that a lot of DRM software just doesn't let legal and valid users play their legally owned game. It could be something as simple as being a programmer and being told by the DRM that you can't play the game because you have hacking tools installed (in this case a debugger). So the company doesn't only tell you how and where you can play your game, it also wants to dictate what other things you do with your machine. And there's also DRMs that let you install the game a finite amount of time, and/or requires authentication via Internet. So, if the company goes broke or decides to bring down the authentication server, you can no longer install that game. Seems to me you are giving too much power to some publishers over you.
Same goes for movies or songs purchased with DRM. DRM enforces some restrictions on you, some bad restrictions that prevent you from using your legally owned media from using it in ways not covered by the DRM. Let's say I legally own a series on DVD, but some years from now the dvd format will disappear into oblivion. So, what prevents me from keeping copies in another formats? I'm not talking about copies that are used to exploit the media simultaneously in different places. I'm talking about keeping the copies for yourself. If there's no DRM, I can do it. But if the DVD or the new media format are DRM infested, then I can't do that, because it's qualified as an illegal use.
So, as you can see, I'm completely against DRM. I'm strongly opposed to letting corporations rule the way I can use things. I totally against letting them abuse me.