E.R., I’m going to assume by “anti-Hoppean” you mean someone who does not agree entirely with Hoppe with regard to “the ultimate justification for libertarian ethics” being his argumentation ethics theory. It would be useful if you could confirm this, and that you are not referring to his theories on democracy, immigration, etc.
I’m not necessarily saying I am in this category; I am still undecided on whether I think AE is valid, or whether it fully acheives what Hoppe claims it does. But this is an attempt to succinctly outline a libertarian “legal theory” not based on Hoppe, as per your OP.
What is “ethical” and what is “unethical” cannot be established through argumentation. There simply is no objective ethics; no correct and no incorrect answers. It is purely subjective; each individual must decide for himself what actions he considers ethical and unethical. Libertarian ethics does not have to be argumentatively justified, because it is merely a matter a personal taste. I might be a libertarian simply because I find theft disgusting, and that is enough.
Now, assuming Hoppe’s theory is valid (and Kinsella makes a very powerful case for it, IMO), it’s merit is as follows. If a socialist is arguing with a libertarian by saying “socialism is an objectively superior ethic”, then Hoppe’s argument proves he is flat out incorrect, because for it to be objectively superior, it cannot contain the performative contradiction that it does; it cannot be argumentatively justified, and this is the only way objective truths can be ascertained, so it is incorrect.
But if the socialist is merely saying that “socialism is a superior ethic” (for some subjective reason, like he believes that socialism creates prosperity and subjectively values prosperity over poverty) then Hoppe’s argument cannot be used. It would be like if the socialist told you “I prefer chocolate ice cream to strawberry”, and you reply that you have ironclad proof, some kind of mathematical formula or something, that proves strawberry ice cream is objectively superior to chocolate. Clearly, the socialist would laugh at this and say “Duh! There is no such thing as objectively superior when it comes to preferences for ice cream! I just like what I like! Subjective Theory of Value!”. Similarly, “There is no such thing as objectively superior when it comes to preferences for ethics; I just like the socialist one the best. Subjective theory of ethics”.
So, essentially the “legal theory” (assuming by that you mean “justification for libertarian laws”) is that libertarian laws are a good preference to adopt, for a variety of reasons (e.g. prosperity, peace, fairness, universality, etc, or justified by considerations about history or evolutionary psychology, etc).