A recent Bryan Caplan post finally crystallized for me why I find so much libertarian thinking and commentary to be irrelevant:
Here's the best way to sum up my outlook: The endpoints of the political spectrum are not the "far left" Michael Moore and the "far right" Rush Limbaugh, but the totalitarian Josef Stalin and the anarcho-capitalist Murray Rothbard.
There is no real prospect of our society or government going anywhere near either of those extremes. (The same cannot be said for the Moore/Limbaugh endpoints.) So discussions that invoke those extremes as arguments for particular policy positions are decidedly unconvincing. They constitute idle theorizing, unengaged with the messy democratic business of policy-making within the margins of real political possibility.
It's that messy policy-making that actually affects people's lives.