... is a political strategy that says if you want to push forward an idea within a culture, then you need one group of people who push forward an idea that is considered "too radical" by the vast majority of people (such as, all drugs should be legal), and when the people who oppose such ideas denounce it as "crazy," you then need another group of people who promote ideas that are considered "more reasonable" (such as, medical marijuana).
Once the "more reasonable" idea is accepted, then the next move is to push yet again in the direction you want to go (such as, now that medical marijuana has been tried and the naysayers were proven wrong, we should make it legal for everyone and tax it).
By having two groups on the same side playing "good cop/bad cop," the ideas they both want to promote eventually become accepted within the culture.
The progressives have been using it for decades, to the point of infiltrating both political parties and most of the Propaganda Media outlets.
The liberty movement needs to utilize this strategy, too. We need anarchists AND minarchists AND "constitutional conservatives" and even "constitutional democrats" (someone kinda sorta like Dennis Kucinich).
If someone who claims to support liberty (*cough* Glenn Beck) at some point comes out with a real anti-liberty idea, then we need to call him out on it. But as long as people are promoting libertarian ideas -- IN GENERAL -- this is a GOOD thing because it WILL have a positive effect within the culture.