Why do so many people write in library books?

[James]

It is really annoying finding a good and then finding out that some inconsiderate a-,hole wrote on every square inch of the book. In my most recent experience, somebody circled and underlined all the answers in a test preparation book. What use does this book serve anymore? How can I asses my lack of knowledge in a specific subject if I am influenced by the other person's answers? (To his/her credit, he/she did pretty well on the test...probably because he/she didn't use time limits.) Why not just take notes or write responses to novels or tests in a notebook? I know it is more convenient to write in the book, but the whole point of going to the library is knowing that (1) the books do not belong to any individual and (2) are intended to be returned in the same condition in a timely manner. Why do libraries not do more to catch people that write in books? It wouldn't be that hard. One would simply have to flip through the book, looking for any drawings or writing.