To my mind, deontological ethics can be the result of either:
(a) belief in objective ethics, where the principles are either of divine/otherworldly origin or the product of a priori reasoning
(b) a process where one posits certain goals, and then determines which ethical principles the universal instantiation of which are most likely to achieve those goals
I take the second route: i.e. I don’t support in the NAP because I believe it was handed down from on high, or because I think it is objectively true, but rather because I know that the kind of world in which I want to live will be most likely to come into being if the NAP is universally instantiated. To my mind, consequentialist ethics are just immature ethics. That is, consequentialists know what kind of results they want, but they haven’t learned enough about the world to know which principles should be universally adopted to best achieve those results, so they have no principles and just aim directly for the goals whenever they happen to see an opportunity. By way of analogy, a deontologist is like someone who knows the behavior of deer and hunts them systematically, with great success, while a consequentialist is a hunter who just shoots whenever he sees a deer, oblivious that there might be a better way of achieving what he wants.
As for the “legal or moral theory” question, I would say both. First there is the libertarian ethic (however one arrives at it), and then there are legal principles that are applications of the libertarian ethic. Libertarian ethics and law should always be in accord. As for Block’s example, I think it’s true that the law tends to be deontological (and should be) and personal ethics tend to be consequentialist (and should not be, IMO). Like I said, the difference between the two is one of knowledge, and it’s no surprise that people who specifically study social interaction (like people who develop law) lean toward the more mature deontological position as a result of their greater knowledge (even if their conclusions are incorrect, they nonetheless develop principles because of more systematic study).