Teachers will go to great lengths to keep their classroom libraries looking nice. Many have checkout policies for borrowing books to prevent them from being stolen. Some even include a kind of temporary barter system by taking something that the student will obviously want back by the end of class, like a shoe.
These teachers are very concerned about their books because they, undoubtedly, have funded them out of pocket from expensive bookstores. New books aren't cheap. But children don't care if you bought your books from Barns & Nobel. Worn books represent loved books. They have been read and enjoyed by many people. Even books without pictures on their covers will find their way into students' hands.
But many children in this country don't have access to books. Many don't have a single book in their home. They may not even be able to make it to the public library safely. There are organizations that work very hard to supply these kids with books to read. But for some, it's too late. Many children already despise reading. It's a horrible truth that hard for me to even think about.
So, in my opinion, if a student cares enough about a book in the classroom library to steal it, someone's doing something right. If a student cares enough about a book to steal it, I believe that they should have it. Sure, the student may not have the proper ethics yet to know that stealing is wrong, but at least they haven't given up reading. At least they have the motivation to want to own something that will lead to their own growth. And perhaps they may get to the point where ethics matter more.
I have a large collection of picture books and young adult novels that I've gotten for cheap from half-priced bookstores and garage sales. I don't even have a classroom of my own yet, I don't even know what grade I'll be teaching, but I've already gotten my classroom library ready to go. And I hope many of my books are stolen.
Edit: My husband says it still promotes miscreant thievery and ill ethics to have these philosophies, even if I don't announce them to my students. Perhaps I will have some sort of no-checkout take-home policy of my classroom library books. I don't want to give books as any type of reward (perhaps other than for simply completing a year in my classroom), and I don't want to have a situation where I'm allowing each student to take a book but "Megan" already took the one that "Jose" wanted because she got to go up before him. I'll have to see what I can come up with.