If today it's "obvious" what's bad; When this generation dies off, who is appointed master of the universe and decides what's bad? It won't be you. It'll be the guys with the money; See Pluton. They're already paving the way for just that (at least in tech and what your wallet must must must spend). But, I digress.
You shouldn't ban books. You should teach morals.
My friend, Swim, who is a Jew living in Israel doesn't support banning Mein Kampf. So much so that when Swim's friend ordered it from Amazon, neither opposed it. Curriculum teaches about Hitler's rise to power and the abuse of his people to do so. That's more than enough to understand not to follow in his footstep. Swim's friend was interested in Hitler's political prowess.
I'm not interested in Mein Kampf. But, if someone is, he most surely has the right to read it. Kill the way some fanatics did because of it? No, that's immoral.
Who decides morality? That's complex, I think. But, I also think it is an innate intuition that lives in all of us.