Ebooks can be purchased as well, with a little skill (or reading a tutorial) you can make it undeletable and uneditable as well.

You’re quite right (at least it used to be easy, I have not checked for some time how hard it is now to get rid of Apple’s and/or Amazon’s DRM… the two main DRM-locked ebook sellers), but keep in mind not everybody feels ok to not respect the rules and/or breach the contract they signed. Also there is no need to that at all with printed books.