Intellectual purity may be satisfying, but it's not necessarily effective:
Every ideological stripe has those people. There are people who argue that Obama isn't a true progressive because of X, or that so-and-so isn't a true conservative because of Y. The difference isn't in the existence of these people, but the percentages of these people. Libertarians seem to have a higher percentage than most other groups, and this may be why we are so ineffective.
Ideological purity sounds fine and good, but it also pushes luke-warm libertarians away. They find themselves in less friendly terrain, often the Republican Party (but not always) where their support is mustered on some issues and ignored on others. They're told by libertarians that they aren't real libertarians, so eventually some believe them.
Most ideologies have a spectrum of beliefs that aren't necessarily the beliefs of all members of that group. There are pro-life Democrats, and pro-gay marriage Republicans. There are anti-gun Republicans and pro-gun Democrats. They function within their respective groups just fine, but libertarians? For some, they require absolute obedience to the ideology.
It's kind of funny though. Libertarians almost universally don't want government to think for us, but some libertarians have no problem thinking for society as a whole by labeling some as “not libertarian”. They don't want to look at the whole and realize that no two people are going to think about the same things.
That's the trouble with labels -- and I think the writer is correct that libertarians are guiltier than those of other political persuasions -- is that they start out being descriptive of a particular collection of beliefs, then end up making them prescriptive;
