That is a copyrighted text book is it not? Any one except the publisher or a bookstore sending you a pdf copy would be commiting a Federal Crime.
Hmm... Is downloading really stealing in the same way as robbing a bank or shop lifting? When you rob a bank and steal money, the money in the bank is not there when you leave. Downloading a book on the internet will still leave the original in exactly were it was the moment before you did make a copy.
After that you can start the discussion wethever it's bad/good or immoral, and maybe also talking about if it's possible to actually own an idea. But for further discussion of that I think there should me a thread in another part of this forum.