I've been thinking about this lately, and I'm not sure where I stand. I'm against book burning, but I feel like there are also problems with unchecked dissemination of ideas.
I think this is flawed logic in a few ways, but I'll put it down anyway:
1. Is there a difference between an undiscerning student (i.e. young, impressionable, hasn't been taught critical thinking, doesn't have sufficient experience to evaluate the validity of what they're learning) reading Ayn Rand on their own and being taught Ayn Rand by a teacher?
2. Would you consider it acceptable to teach Rand's novels non-critically as part of the curriculum (heck, why not, there are more than a few Senators that cite her books as inspiration).
The problem I run up against is how do you "objectively" decide which books to restrict. As you said, "school libraries curated by legislators with an agenda seem like a Really Bad Idea," but everyone has some sort of agenda. Everyone thinks it's obvious what should and shouldn't be taught in school, but of course it's not the same "obvious" for everyone.