Are you confused because you believe that libertarians are on the right, maybe? If you examine libertarian positions, you might be surprised to find many of them "left" of Obama.
There are some issues which aren't fiscal (directly) but aren't really social policy (directly), where Libertarians are the farthest "left" (or right, or whatever) of the two big parties, and where people may vote based on morality.
GTFO Afghanistan ASAP (and their overall isolationist position) is one of the big ones. I could see someone who was pro-state intervention in domestic life, pro big taxes, etc. still voting Libertarian if he thought GTFO Afghanistan ASAP was the most important issue.
It's basically impossible to put US politics (or anywhere, really) on a strict left/right linear chart.
