While I grant you that those promoting DRM may in fact start from the premise you state, the end result is that we all wind up being treated as potential thieves. Perhaps it is an overly cynical attitude... but that is how I view it.
"the end result is that we all wind up being treated as potential thieves"
We all are potential thieves from the perspective of anyone who doesn't know us; and if you have a valuable good, it's a far more reasonable (and profitable) assessment than "no one is a potential thief." It's the same stance you take when you design a website: "everyone is a potential hacker."
A potential thief, however, is not an actual thief, and to repeat what I said above, I don't believe DRM treats users as actual thieves: it treats them as potential thieves until they've authenticated and as honest users afterward. If you have to authenticate annoyingly often, it's a usability problem, but it doesn't change the essential dynamic.