Are they completely non-curated? Kids just put whatever book they want there? If so I'd say the teacher isn't liable for what happens. If the teachers put the books or manages which books are there they are curated and that activity can be managed by the people paying the teacher, ie the taxpayers/representatives.
There's also the fact that you're selecting for some of the worst teachers by confining them to curriculum and harshly punishing deviation or expansion. The best teachers are good precisely because they do those things, and if you take that away it's not the same job anymore—they're just reading a script and serving as a mouthpiece for the state rather than serving the students the best they can. That's not what they signed up for. They'll leave.
Check teacher forums, this kind of over-management and micro-management are major reasons for discontent in the job, and one of several factors pushing good teachers out of teaching.
> and that activity can be managed by the people paying the teacher, ie the taxpayers/representatives
In this case, Florida has decided to manage that activity by making it a felony to merely happen to have a book on the shelf that's not on the pre-approved list.
