The way I see it there are differing contexts for thinking of purity. For sake of convenience (and alliteration) I'll refer to them as practical and principled purity.

As long as there's a nation-state or some similar band of thieves conspiring to rob peaceable individuals of their lives and property, practical purity -- being able to act in total, consistent purity with one's principles -- is impossible. As just one example, an individual in the USSA, no matter how self-reliant, simply cannot avoid all taxes.

Principled purity, to me, means presenting a consistent view of how full liberty might be accomplished. It necessitates thinking about what one's principles really are, what one values down at the root of his being, and communicating that (if desired). Not only is this excellent mental exercise for those who engage in it, but it also helps ensure that those who do communicate with others about the value of liberty present a consistent message to them. (It may not matter much at the beginning, but it will likely matter at some point in the conversation.)

After all, many Americans already tend to think of libertarians (mostly because of what they've heard from the LP and assorted loud, er, eccentrics) as libertines, or in some other negative way. It doesn't help our efforts to educate, or to distinguish ourselves as more principled, if we're advocating/supporting actions that betray those principles.