According to his Facebook page (who knew Facebook was so popular that even attempting murderers use it to tell the world a little something about themselves?!), he was a humanist. Let’s look at what humanism is, briefly. In a nutshell, humanism is the arrogant belief system that utterly rejects religion as the basis of morality. Humanists basically believe that without God, human beings can still be innately moral or ethical; this is nonsense, of course, since from where but religion do morals really come? Because of its arrogance, humanism counts a lot of liberals/communists as its adherents. Just a few examples are Noam Chomsky, Karl Marx (commie), Bill Maher, Christopher Hitchens, and Friedrich Engels (another commie), all of whom we can safely agree are despicable people. I think that Duke basically showed the world that, contrary to humanism’s principles, human beings can’t be innately moral without God.
Next, Duke was also a fan of the movie "V for Vendetta." Anyone remember that film from a few years back? Well, guess what, if you were a liberal, you probably loved it. According to Alan Moore, its author (the movie was based on a graphic novel), the movie was an "American liberal fantasy about someone with American liberal values standing up against a state run by neoconservatives." If you’re a liberal, that’s pretty darn damning for you because there is now a connection between violent shooters and a movie like "V for Vendetta" that espouses a lot of angry liberal values.
Finally, again on Duke’s now-removed Facebook page, he hatefully complained about being born poor and how much he not only blamed the wealthy, but accused them of cheating him and, I guess, "oppressed" people like him. From that belief system alone, he sounded like he could have been a perfect candidate for the bottom-up, top-down radical plan of socialists like George Soros. Glenn Beck talked a lot about that strategy. Basically, it entails that socialist radicals in a government (such as those we know are in Obama’s government) continually anger and provoke the so-called downtrodden masses, of which Duke was a part, by feeding them class warfare propaganda and the like. Then, they finally snap and do violent and radical acts, which Duke certainly did, which is when the so-called top (government) comes down to control citizens all the more.