I use and love Steam, however I'm against forced activation of any kind. There are people who don't want Steam and don't need it. People who want nothing to do with it. And its a pretty sizable group. They won't use Steam for anything, so all it'll do is sit there, take up space, and use resources. And yes I know Steam barely uses any resources, but when you won't use it for anything, thats what it does.
Consumers should have a choice. And forcing them to use any system, no matter how good or bad it is, is wrong.
I wish more games would go the Unreal Tournament 3 route with activation systems, where you can choose to install it using Steam if you want, but you don't need to do so to play the game.