I became somewhat of a regular reader of the BHL blog recently. I think their stuff is interesting, but I also think they could improve their persuasiveness to their target audience (and I am assuming I am not misidentifying their target audience). Most of that audience does not have formal training in legal theory. Even I, who have some formal training in lots of things, found the BHL critique of Hoppe's argumentation ethics confusing. That's why I'll try to provide a translation in terms that are more understandable to those to whom this critique was addressed. Again, since the critique itself was confusing to me, what I am going to provide here may not be an exact translation but rather a different critique altogether. In any case, here we go.
Hoppe's paragraph that the BHLs quote is this:
It must be considered the ultimate defeat for an ethical proposal if one can demonstrate that its content is logically incompatible with the proponent’s claim that its validity be ascertain- able by argumentative means. To demonstrate any such incompatibility would amount to an impossibility proof; and such proof would constitute the most deadly smash possible in the realm of intellectual inquiry … Such property right in one’s own body must be said to be justified a priori. For anyone who would try to justify any norm whatsoever would already have to presuppose an exclusive right to control over his body as a valid norm simply in order to say ‘I propose such and such’. And anyone disputing such right, then, would become caught up in a practical contradiction, since arguing so would already implicitly have to accept the very norm which he was disputing.
My interpretation of this paragraph is as follows. The fact that you try to argue with someone, lets call him Jim, implies that you recognize his exclusive ownership over his body. Also, you need to have exclusive ownership over your own body in order to be able to argue anything. So, if Jim says: "I have the right to say that the sky is red," and I try to argue that Jim does not have the right to say that, Hoppe would claim I am engaging in a practical contradiction because I am, in fact, respecting Jim's right to say the sky is red, since I decided to argue and not to physically attack Jim.
The problem with this logic is two fold. First, it conflates the ability to perform an action with the right to perform an action. Second it conflates the choice to not attack someone physically with the obligation to not attack someone physically. Just because Jim has the ability to say the sky is red, this does not mean he has the right to say that. Just because I chose not to attack him physically when he said the sky is red, does not mean I am fulfilling an obligation to respect his right to say the sky is red.
Suppose Jim actually did not have the right to say the sky is red, but, instead of cuffing him and locking him up, I decided to try to explain to him that he did not have the right to say what he said. He may have been confused. In this case, my generosity was misinterpreted as a recognition of Jim's supposed right. Thus, no practical contradiction occurred in this case.
Suppose now, instead, that Jim did have the right to say the sky is red, and I knew that he did have that right. However, for some reason, I don't like it when he says the sky is red. I may try to attack Jim physically in order to stop him from saying the sky is red. However, this may carry risks I don't want to bear. In that case, I might try to fool Jim into believing he does not have the right to say what he said. Thus, I may argue with Jim about his right to say the sky is red, and if I am skillful enough, I may succeed. Again, I am not committing any practical contradiction. My choice of a strategy to shut Jim up was misinterpreted as my respecting Jim's right to say the sky is red.
We could come up with other scenarios as well, but I think this is enough to illustrate the message.