Amendment I, United States Constitution
Surprise, surprise: Mein Kampf was one of the best-selling political e-books of 2013. It is not protected by copyright, even in translation, and it's widely available for free, though you can also pay a lot of different publishers 99 cents for it. (I wish that everyone would agree that Yad Vashem is the only organization with the right to take any money for it, though they probably wouldn't want to sell it.)
If you were looking to ban some books, Mein Kampf would be a logical place to start. Instead, Mein Kampf is Exhibit A for the value of the First Amendment, and why it's never a good idea to ban any book, no matter how offensive its content.
I have not read Mein Kampf, but had I continued to study German history, I definitely would have read at least parts of it. I probably would have read parts of it if I'd stayed in political communications, and I might eventually take a look at it just on general principles. Like The Quotations of Chairman Mao (which I have read big excerpts from, in translation), it's a document that made a disproportionate impact on a vast number of people. It's important to know what's in it, and understand how the rantings of a racist megalomaniac could have captured the imaginations of entire nations. The Nazi propaganda machine was one of the most effective in history. Anyone who wants to block similar movements in the future needs to understand how the first one worked.
It's also important to keep hateful literature available because of the confirmation bias phenomenon I wrote about earlier this week. If hate speech is suppressed, the rational non-haters cannot speak against it in public forums. Suppressed speech doesn't go away; instead, it oozes into corners, it collects underground, it seeps to the edges of society and is cherished by people who love secrets and conspiracies and already believe they are persecuted. It builds up under pressure and explodes when good people least expect it, because it was all happening somewhere we couldn't see it.
Did the "Duck Dynasty" guy have a right to say hateful, stupid things about African-Americans and gay people? Yes, he did. Did A&E have a right to fire him for being an embarrassing ignoramus? Yes, they did. That was never a First Amendment issue. But is our society damaged by giving him back his television show? No, I don't think so, because it's no bad thing to remember that he speaks for a lot of other ignorant, delusional people. His continued presence in the public eye keeps the conversation going. Since he's on the wrong side of history, that conversation can't do anything but embarrass him and A&E more. I wasn't watching "Duck Dynasty" anyway.