Thanks to Mickey Craig for calling attention to this article, which, while interesting, proves nothing. That there can be no such thing as a person who is simultaneously an economic conservative and a social liberal is demonstrably false. There are thousands of such people, and they call themselves libertarians, or classical liberals, or something of that sort.
More importantly, the author here is making a very bold claim, but basing it on the narrowest of samples--the current makeup of the United States Senate. It does not even extend its analysis to the House, where the author would at least have to deal with Ron Paul (R-Texas), a former Libertarian Party candidate for president.
The real question, it seems to me, is not whether or not "libertarians" can exist, but rather why there are none in the Senate. My hypothesis is that it has a great deal to do with the amount of fundraising that must be done to be elected at a statewide level. The pressure groups that keep Republicans and Democrats alike in office have little interest in supporting true mavericks. A consistent liberal, or a consistent conservative, would seem to be a far safer bet.
Im certainly willing to have this hypothesis shot down, but the argument that a survey of the Senate establishes that one cannot be economically conservative and socially liberal is unconvincing.