I agree that this is certainly a concern, everyone has a bias and we should be aware of it. On the other hand this bias isn't always bad. A librarians bias pres

I agree that this is certainly a concern, everyone has a bias and we should be aware of it. On the other hand this bias isn't always bad. A librarians bias presumably comes from reading hundreds of books and years of education. If they think an unpopular book is worth saving presumably it is because the book has a high value for the few people who do read it. It also comes down to trust in the librarian, presumably in the interview process you try to make sure you are not hiring an outspoken Nazi. If you do hire a Nazi librarian they have many other ways of injecting their bias by inviting speakers, recommending books etc. so it is still going to be an issue even if they aren't picking what books you have.