I've commented at length on my blog, but in short I'd say the major disagreement that you still seem to be standing on shaky ground with the idea of objectively determinable - i.e. you can't go from possession to ownership (as in, I'm being robbed, someone is taking my property) and still call that plainly objective with a context within which to define ownership.
I dunno. Maybe I'm just not being clear.
First, any short article has to take a lot for granted. The best I can do is try to be explicit about anything controversial I'm taking for granted. It's not really helpful to say, "Well, you have no justification for taking this or that for granted." Well, duh. That's what it means to take something for granted. The question is, how does taking or not taking this or that for granted actually change the argument? The same goes for distinctions of convenience. How does making a different distinction affect the argument? Louis and Horowitz do point out that yes, I'm taking things for granted, and yes, I'm making some distinctions of convenience that might have some gray areas, but I don't see in their work how it affects my argument.
More importantly, I do not go "from possession to ownership... and still call that plainly objective." Louis is skipping over the important bit. I explicitly define ownership as subjective and socially constructed. The question is, how do we evaluate social constructions? One method of evaluation is to say that we can socially construct political judgments (judgments of justice and injustice) only on the basis of objectively determinable facts. If we make different socially constructed political judgments about two situations where the relevant objective facts are the same, we are being inconsistent or hypocritical. Another method of evaluation is to say that we can socially construct not only on the basis of objective facts, but also on subjective facts, such as agreements, laws, etc. If we have agreed, for example, that citizens must pay taxes, or that renters must pay rent, then that agreement becomes relevant: we can consistently and non-hypocritically have different political judgments of two cases with the same objective facts, because they are distinguished on subjective facts, i.e. we might recognize that an agreement exists in one case, and no agreement exists in another.
I want to emphasize again that I do not believe that political and ethical judgments must necessarily be objectively consistent as in the first case above. I am introducing the distinction because I have with my own ears heard Libertarians argue that taxation are objectionable, regardless of any social constructions, because it has the same objective facts as other cases we judge as unjust expropriation. They also argue, however, that enforcement of agreements is permissible, even though they have the same objective facts as unjust expropriation, because of the existence of the social constructions of agreements and ownership. There are, perhaps, other ways to argue for the superiority of ownership, but arguing that social constructions in general cannot establish justice-relevant facts when one does not like a particular construction, and arguing that social constructions in general can establish justice-relevant facts when one does like a particular construction, is self-contradictory.
This distinction goes right over Louis's head:
Secondly I'd suggest that your analogy between taxes and absentee ownership (both being social constructs) isn't a valid analogy. In fact I'd suggest it's a category mistake. Yes they're both social constructions, however the initiated coercion is not against a concept of ownership in both cases. i.e. while they are both social constructs (which all ownership is), they are not both representative of the initiation of coercion against ownership. If I own property, whether directly (in that I, e.g., live there personally) or as an absentee owner, then what I do with that property is to a certain degree my business. If I’m an absentee owner renting space to an individual who fails to pay his rent (and we have some sort of rental agreement), then through coercion I’m going to kick him out. Now to make the analogy work with taxes it would have to presuppose that the government “owned” the money it was taking, but in fact it doesn’t. That we socially agree (to one extent or the other) to pay taxes does not entail ownership over that money and therefore the analogy fails.
Why should it matter that we label one social construction as "taxation" and another social construction as "ownership"? The choice of label seems the most specious distinction possible to make. If we can socially construct the concept of "ownership" to justify coercion, then we can just as easily socially construct the concept of "taxation" justify coercion. (If Louis is especially hung up on labels, then I suppose we could just change our socially constructed notion of ownership to actually give the government ownership of our money.)
Andrew reveals the crux of his argument and the relevance of my analysis: we "have to presuppose that the government “owned” the money it was taking, but in fact it doesn’t [emphasis added]." What facts, precisely, is Louis referring to here? Objectively determinable facts, in which case my argument about whether subjective social constructions must strictly supervene over only objectively determinable facts or whether subjective social constructions can create normatively relevant facts is directly pertinent.
Alternatively, Louis might simply be saying that some social constructions, such as ownership, are in some sense per se factual; some social constructions, such as as taxation, are in some sense per se non-factual, fictitious, or delusional. Another approach might be to say that some social constructions are per se privileged over others: the socially constructed concept of ownership inherently supersedes taxation.
Or maybe Louis has just had a revelation from God.
Perhaps someday, I'll see a Libertarian offer something better than argument from vehement assertion. I've given up on either Louis or Horowitz giving something better.