It's actually completely reversed. DRM is much more like placing a policeman in your house to watch what you do, just in case you decide to do something illegal. I.e. since DRM is present on your own computer and in your system, it's like an intruder whose purpose is to spy on you and treat you like a criminal. I doubt many would find it ethical if a police camera would be placed in their own home, yet for some reason they accept DRM as a normal practice.
Let's run with that analogy for a moment. When you buy a physical item, the store doesn't need to send a guard to watch what you do with that item, because once you give it away, you no longer have it. There is one item, and you can't have it in two different locations.
Digital items are a completely different story. You buy a digital item, and you can make 2, 20, 200 or even 2,000,000 copies, and still have access to the original. I don't believe DRM does anything to stop the truly determined, so I'm not arguing for DRM, but at the same time I can understand corporations that want to at least place a measure of security to prevent casual copying. Ultimately, Steam's DRM is the least intrusive of any of the choices out there, and I - for one - am perfectly content to accept it until such time as it proves otherwise.
