It's generally understood that you DON'T use the library's copier to duplicate an entire book.
It's generally understood that you DO use publicly-accessable shared-directory peer-to-peer software to duplicate an entire file.
There's a difference.
I think that's only a matter of simple economics and ROI. 250 pages at 15 cents per is likely much more costly than just buying the book. General understanding doesn't have anything to do with it -- the option is available and I (er, I know a guy) who have done it.