Many of my colleagues are reading Brian Doherty’s "Radicals for Capitalism," so I read the first chapter.  Doherty describes how movement libertarians competed to show who was more devoted to principle: 

Many a movement libertarians’s favorite pastime is reading others out of the movement for various perceived ideological crimes.   As Fred Smith, head of the libertarian think tank Competitive Enterprise Institute, says, "When two libertarians find themselves agreeing on something, each knows the other has sold out."  Libertarians are a contentious lot, in many cases delighting in staking ground and refusing to move on the farthest frontiers of applying the principles of noncoercion and nonaggression; resolutely finding the most outrageous and obnoxious position you could take that is theoretically compatible with libertarianism and challenging anyone to disagree.   If they are not of the movement, then you can enjoy having shocked them with your purism and dedication to principle; if they are of the movement, you can gleefully read them out of it.

Libertarians … have advocated … private ownership of nuclear weapons; the right of parents to starve their children; and that if you fell off a building and grabbed onto a flagpole and didn’t have the explicit permission of the person who owned the balcony, you ought to let yourself fall rather than violate their property rights by crawling to safety. 

Seems quite a bit like arguments leading to duels.  Duels signal ability and willingness to defend yourself, which women find attractive because it suggests you can and will defend them.   Perhaps women like men committed to principles, in the hope that such men stay more committed to their women as well.