I can't believe I'm stepping into a DRM discussion, but...
I know a few of those Aunt Mabels who might try to share a book with DRM and not know WHY it doesn't work; just that it doesn't. Unfortunately they are the same ones who might then just google the title, end up on a torrent site, and download it illegally. Because "it must be okay if I can just click on it and get it." Just saying, clueless people are clueless. And that works in both directions.