While I don't think that this book harmed me in any way, it wasn't the masterpiece of all time, either. It seems that proponents of the book are just as vehement and unwilling to see the other side as the parents who don't like the book. Some people love the book, others don't. But, I wouldn't recommend it, either. But the Holocaust is frightening and terrifying, and the student you mention as being strongly disturbed by Weisel only responded as most of us would.
Good literature can disturb as well as enlighten and please.