Is it ok for any books to be placed in schools?

It's a good question, to which I think the general answer is to leave library decisions up to the well-educated school librarian, and teaching up to a well-educated teacher. This is not a form of authoritarianism, but a way of expecting these poorly paid people to get on with their jobs. The banning of books has always been a politicized move, by those who want to manipulate the schools. Many of these people are pushed by their churches or political interests. Parents can discuss books with their kids. Banning books also draws attention to them, as if they are dangerous. Kids love that and will easily get access to these banned books, especially because most resources are online. (They see much worse online.) The history of banned books is informative of the ridiculous religious and political double standards for banning books. We're discussing this now only because banning books has become a political motivation by the GOP. To explicitly answer your question: I think that almost any book can be in a school, unless it promotes torture or unjustified murder (eg. to allow for the problem of 'justified warfare').