Libertarianism is more compelling than Anarchism, because it stands for something (for liberty) rather than simply being not something (without a ruler).
Cataphatic > Apophatic. 
Discussion
Yeah that's a decent way to view it. My only objection is in how people will define "Libertarianism" it is far more flexible seeming than Anarchism.
Libertarianism implies personal responsibility, which implies working for others for selfless reasons. AnCap/Objectivism neuters this important aspect of soceity
Couple things-
AnCaps represent a subset of Anarchists
(A small and relatively recent minority of an historically left line of thought)
Objectivists have more in common with (small L) libertarians, but forgoes the "selfless" tortured logic by wrapping it up into one's calculation within rational selfishness.
Last thing.
What is Watts referring to as Anarchist?
I see what you are saying. Having something positive rather than only deduction of what something is not (Cataphatic > Apophatic).
The error is that ALL forms of government are slavery and when slavery exists even in the smallest forms then Freedom cannot exist. As only in a complete removal of all master - slave dynamics can Freedom be experienced. It is all or nothing. It is definitive.
As the idea goes: the slave gets beat only one day a week as opposed to seven days a week. It is still slavery.
I think if this is considered you might change your mind.
The joke is "What is the difference between a Libertarian and an Anarchist?... about 6 months."
And Autarchy takes it to a whole new level...