Luckily DRM (at least the mobi pocket ones) can be removed
On that point, DRM are totally useless on preventing illegal diffusion. They just mess up with customers who don't know how to take them off.
I did't pass my E-book to anyone, it's just mean to spare me the bother of having to deal with pid's. Else, every time you get to reinstall windows, get a new reader or whatever, you need to update the pid list on every website you buy E-books from, redownload your entire collection of e-book.
When I buy an E-book, I don't want to be considered as thief. I'm a customer, and expect to be treated as such, not as a hacker.
If you try to make using the legal stuff a pain, don't be surprised you customers turn to the illegal, easier way.