It's important to remember that the power of Mein Kampf lies in its status as a symbol, not its actual contents. Nobody actually reads Mein Kampf, nor have they ever (just like nobody actually reads the Bible unless they're actual preachers). It was (and still is) about the personality cult of a strong man and his message of power via blaming and oppression of minority groups, not the actual words themselves. People remember only simple things, and like simple reasoning and solutions, which is what made him popular in the first place.
So the banning of this book was an attack on the symbol (and only incidentally on the literature), and the banning of the symbol is of questionable value since it basically causes a Streisand effect. Banning a symbol only adds to its power. It might have been better to just ignore it, and instead focus on prosecuting the actual hate crimes themselves.