I used to believe, that legislators used a outdated model of intellectual property. Unfortunately I am wrong, after all if I buy a book I am allowed to modify t

I used to believe, that legislators used a outdated model of intellectual property. Unfortunately I am wrong, after all if I buy a book I am allowed to modify the content, by writing in the margins or by tearing out pages. ( I may even make a collage, using several pages of the book.) At least as long as I do not sell or perform my modifications. So I wonder, why I am not allowed to do the same things with software? Linking another library is simply not different than gluing the first half of Lord of the Rings to the second half of the Cryptonomicron.