National defense, i think we both agree, is one of the very limited set of roles the federal government has. Patrolling the air-space to ensure against terrorist attck using commerical aviation is a reasonable facet of national defense. I therefore doubt that even the most purist of libertarians would not concede that the federal government might have a legitimate role in airline security.
On the other hand, we would probably also agree that the state, given any role, will try to expand that role beyond all reason. it is therefore reasonable to say that while we want the airlines secure, we don't want the state levying a 50% income tax for 'airline security', since given the chance they'll try to define welfare and crop subsidies as an essential element of airline security. We have to limit the resources they have to provide airline security, and the scope of that activity.
A legitimate part of that scope is identifying the most likely sources of danger. Scimitars are more a danger than plastic spoons. It would be silly to treat them the same. And similarly, little old ladies from Peoria, as well as comely young conserative women, don't hijack airplanes, as a rule. We have excellent evidence for this. On the other hand, a high proportion of terroristic hijackers are Arab men. Giving the latter a thorough screening would appear to be a minimal part of airline security. Giving Ann Coulter the same screening is an expansion of the role of the state - we're out of the security and into the 'equality' business - and a waste of resources.
I understand, of course, why somone might want to go through Ann's undies, but IMHO it's a little fetishistic.