On Contradictions Between Philosophy and Action
Another problem that I see with the attempt to prove "self-ownership" and "property rights" as an a priori axoim that is inherently established by the act of argumentation (as Hans Hoppe's argumentation ethics seems to essentially be) is that a contradiction between one's philosophy and one's actions does not constitute a "proof" or "disproof" of a given philosophy in and of itself. It may be proof that the person in question is being hypocritical, but that doesn't necessarily disprove what they are argueing. This is also a problem with Stefan Molyneux's "UPB".
Someone could concievably argue in favor of liberty while violating the liberty of others in their lives or argue in favor of tyranny while mostly being benign towards others on a personal level. But consistency between one's philosophy and one's actions is not a proper measure of "truth", it is the measure of hypocrisy and dishonesty. A hypocrit could theoretically have valid arguments, while an honest person could theoretically have invalid arguments. A man's honesty and integrity, strictly speaking, is not the measure of the "truth" of his statements, it is question of the character and style of a person. There is no absolute correlation between the truth value of a proposition and the character of the person who makes the proposition.
It also doesn't seem to make much sense to posit that what you believe is inherently presupposed by everyone else. Someone could concievably sincerely believe that "slavery is moral" or "morality doesn't matter" and they could concieavly argue those premises without necessarily contradicting themselves. People do not necessarily presuppose your premises by argueing. And even if the behavior of argueing in some sense contradicts what they are argueing, that is does not inherently nullify their argument. One has to explain why their argument is false, and the fact that someone's behavior is hypocritical does not constitute an explaination, it only begs the question and is not directly relevant to the person's argument as such.
What a curiosity: the presupposition that your presuppositions are presupposed by everyone else! What circular logic such an a priori intrinsicism ends up being. By argueing with you, I implicitly prove you correct? Do people not realize how abusable such a method is? One could theoretically use it to justify just about anything, since it essentially means that one's premises are simply assumed to be absolute and universal truths without actually having to explain why. Hence, one can avoid questions and criticisms of one's premises by simply brushing them off as inherently being disproven upon utterance, while you yourself have not argumentatively demonstrated the case for your premises. Noone should take that seriously.