Ezra Klein and Will Wilkinson talk about "liberaltarians" on BloggingHeadsTV. Ezra (the liberal) starts if off by asking Will (the libertarian) why libertarians are so interested in philosophy. Will, toward the end, tells Ezra he's trying to "open [him] up to the beauty" of the free market. Ezra -- despite a very long, chatty diavlog -- is not buying.
ADDED: I think -- after tangling with a lot of libertarians a few weeks ago -- that the reason -- excuse the expression -- the reason libertarians are so interested in philosophy is that their ideas look best in philosophical form. It's the same reason fat people wear dark clothes.