So, two things come to mind here.
First, what you're saying is that we shouldn't be able to take full advantage of all the added benefits of digital content. See, with a physical book, I can read it and lend it out or sell it. I can't keep a backup copy in case it gets dropped in the tub. I can't search it for keywords (easily). I can't expand it to fit an indefinitely large number of notes per page. Ad infinitum -- digital content is simply more flexible than physical content.
You seem to be suggesting that this should be stifled. The content providers should be provided with a guarantee that customers can't exceed the boundaries previously set by physical books. But this is nonsense: the limits on books are there inherently, because the technology (printing) doesn't have the capability to do the other things. When you *have* that capability, then to restrict it is a restriction, not a benefit.
The second thing that comes to mind is that you seem to think DRM can be transparent to honest customers. I must argue against this. We could look at fringe markets if you want (Linux users rarely get the DRM software, and of course it's never open source. What if someone creates a new OS and it isn't as popular as Linux? They're out of luck, right?). But I think that mainstream markets also exemplify the problem. Say you have a system where I can sell an e-book to my neighbor. You revoke my license and provide him a license. Somehow, whether it's through a website or a piece of software, I must perform some additional action to sell my copy above and beyond handing them a CD with the file on it. In that situation, I believe that no DRM, no matter how unobtrusive it is when reading the book, can remain hidden. Compare this to either a physical book or a non-DRM e-book. In either case, the only task I have to sell it is to transfer my copy in any suitable way to the person I'm selling it to.
A related problem is that of fair use. Parody is provided as a fair use. As is classroom use, and others (I'll let you look up fair use, but the basic idea here is that copyright is not an absolute right, but a privilege bestowed by the state to encourage authors and artists to make more books and art). With a tape or non-DRM'd music, I can remix and parody, use it in a classroom, or anything else. Of course, illegal activities are possible, but that is just a fact and nothing can be done about it except to sue someone who does something illegal with it (the RIAA seems to have figured at least this much out). For books, taking notes on the margins in a digital situation probably requires modifying the file. This is perfectly allowed under copyright (for software, you may have problems with the EULA, but even that is of questionable legal value). I believe, from both past experience and some thought experiments, that any DRM system that has any effect at all cannot permit such uses by either logical, legal, or practical necessity.
The burden of proof is on you now -- show me a DRM system, even hypothetical, that could remain hidden to the end user, open source, and still allow the continuation of the first sale doctrine, remixing and parody, and other fair uses. (Because this is exactly what I get without DRM)