Lawrence,
There are books and reference materials posted in the internet for free which does not violates the author's intellectual rights. for example in the link provided above there a lot of excellent materials that a beginners like me can learn. I will assume that the website hosting the books are sharing them legitimately.
Moreover there are people like me who are not gainfully employed yet that even paying for a $5 book is hardly feasible so we rely on free downloadable reading materials from the net to acquire further knowledge.
I've learned that typing in the subject matter in google and appending pdf will provide tons of links, and most likely/luckily one of those will provide a free download.
I agree with you that it will be stealing if the source is illegal like if you get it from sites hosting pirated materials or for example downloading it from bitlord or torrent sites.Or maybe if someone bought a copy and share it with me, then that would be stealing too
Thanks for the warning anyway...