The problem is not simply, as Smith thinks, that we cannot posit an adequate hypothetical author. It is that, even if we could, the law that would result would be a hypothetical law (whose violation would presumably be punishable by hypothetical incarceration).
Try this hypothetical instead: Two persons who speak only English see sculpted in the desert sand the words “LEAVE HERE OR DIE.”
I suspect that the desert he is talking about although he pretends only to be proposing a "hypothetical," is an allegory for the present state of our legal culture, which is what T. S. Eliot would have called a Waste Land.