I know one writer for a fact that is NOT a liberal! Paging Snake65!
Then there's Johnny Ringo who used to hang out here, not sure when he left or why, good action sci-fi though.
To quote the Duke: "That'll be the day."
There's a mix, as in all professions. I'm quite conservative, my editor is a red diaper baby NYC liberal, and I know authors from all over the spectrum. When we get together, we tend to talk books and ideas rather than politics - but I get along best with those on the conservative side. I agree with some of the others that if anything there's a libertarian streak to SF authors.