This is an excellent explanation of the most fundamental defect in anarchism and libertarianism!

As a much shorter rule of thumb, I find it useful to ask, of any system of governance, "by what mechanism does it resist free riders and exploitation of individuals?"

Anarchism obviously fails because it has no mechanism to prevent individuals from exploiting each other. The mechanism is basically wishful thinking: "What if we all agree not to amass power and use it against each other!"

Libertarianism fails in a slightly less obvious way because it has no mechanism to prevent negative-sum-game outcomes where individuals degrade the commons to their own benefit. (Hi, "negative externality"!)

But a lot of other systems fail too.