While the internet is not policed (and God forbid it ever should be) then anything that is posted on it is fair game as I see it.
Borrowing books was mentioned. If I join my local library for the express purpose of borrowing a book, I have to produce ID before I can join and in that way the library knows where every book is and who has got them.
If the library wasn't policed in this manner people would just walk up and take what they want.
Rioters in London recently took what they wanted because for a time they (the rioters) weren't policed. If it's free, people will take it. It's plain human nature.