I have an MLIS, and worked in libraries for years. It's a common misconception that librarians choose books they think are best, or most morally or intellectually instructive for readers. This never happens, or almost never happens. They buy and lend books that the community has asked to read, or which they believe the community wants to read, based on, e.g. popularity. There's not a council of elders deciding what you're allowed to read.