The Pico case ended with a fractured plurality; five justices sided with the students, but they couldn't agree on a reason.
Pico is a weak precedent, therefore not binding on lower courts. Someone didn't do their homework here.
The Vonnegut family has sued the State of Utah. SLAUGHTERHOUSE-FIVE is banned in a few school districts.
Seriously? The book has sold millions, and continues to be taught in schools across the country. These "bans" will do nothing to suppress this book. It's not hard to find.