You should really read this great piece by Dan McCarthy on James Burnham. Machiavelli was a realist, and of course was despised for being one.
But the most interesting thing to me was the influence of Vilfredo Pareto on Burnham. Pareto pointed out that every society that has ever existed has had an elite. But when a rising elite is struggling for power with an existing elite, it will often use anti-elitist language to inspire its followers, since "Give us power" is a slogan unlikely to attract many supporters.
Contemporary libertarians might ask themselves, "Is there a rising elite class who is using our idealism and energy in an attempt to gain power?" (Ahem, ahem, Koch Brothers, Peter Thiel.)