> making a claim about what libertarianism is is necessarily suspect
You're right, libertarianism is really an umbrella term for many schools of economic, political and other philosophical thought. I'm simply representing what I found to be the most established and logically consistent tenants of said philosophy.
> Are the principles deduced from empirically evident reasoning, or is it as questionably axiomatic as any other system?
I'm speaking to the works of Ludwig Von Mises (along with Murray Rothbard) and his work on Human Action, specifically the development of Praxeology and Catallactics -- which are derived from the Action Axiom. I would say the core tenants of Austrian Economics are very much observable and repeatable, much like game theory.
> Furthermore, neither this sentence nor your economics analogy actually refutes my essential claim that the inability to evaluate and reason at anything other than the individual level makes it impossible to speak usefully about groups of people.
Sure I did. Microeconomics is a counter-example. There's also game theory and personal psychology. I guess it depends on what you consider useful.
> The empirical evidence is that groups have significant effects on people. It is quite clear that it is extremely rare, if at all extant, that people can be defined without relation to a group.
I guess I concern myself with the the largest of these groups, the human species. While cultures and economic landscapes change, the basic tenants of Praxeology and value-theory do not. Preference and desire is present in all acting humans, and I think these realities can be best used to explain why actions are taken.
> That leaves libertarianism and its radical individualism very suspect, from an empirical point of view.
I'm not claiming individuals don't act differently based on their setting and peers, just that these phenomenas can be observed at the individual level in an empirical fashion. If it isn't, then your group knowledge is limited.
> To be frank, that's not a philosophy at all. That's a model.
Yeah, it's a big tent..
> You have to present a third alternative to show it's a false dichotomy.
That I didn't make an incorrect statement?
> Libertarianism, as I understand it, is founded on the claim that the word "liberty" has an esteemed place in the structure of the world.
I would argue that libertarians believe in the antithesis of authoritarianism, and that they have economic and philosophical principles for believing so. While governments and corporations are groups of people, the fruits of their actions can be better analyzed by the actions they take and not what they call themselves.