Thinking about property -- Aquinas

I've been thinking about private property and moral obligation lately. We (by which I mean Americans, or possibly citizens of affluent countries in general, but not philosophers) tend to think that our moral theory needs to keep fixed the system of private property at the bottom of our system of production -- helping out the poor is all well and good, but unjustified taxation is theft, and so on. (Yes, your socialism alert should have just gone off.) Some Libertarians -- Nozick is a good example of this -- actually try to base a theory of political justice on our property system quite explicitly, talking about how every individual owns themselves. (Though doesn't Nozick also say that you're not allowed to sell yourself? It seems like nonfungible property is a contradiction of terms in our system of private property.)

But, of course, our private property system -- like our system of production -- is a relatively recent development. And it certainly wasn't taken for granted throughout most of the last century. If we (ethicists and political philosophers now) purport to give more-or-less universal standards of justice, it seems weird to think that we have to take the economic system of one particular historical epoch as fixed.

Here's a nice quotation from Aquinas, via Peter Singer:

Now, according to the natural order instituted by divine providence, material goods are provided for the satisfaction of human needs. Therefore the division and appropriation of property, which proceeds from human law, must not hinder the satisfaction of man's necessity from such goods. Equally, whatever a man has in superabundance is owed, of natural right, to the poor for their sustenance. So Ambrosius says, and it is also to be found in the Decretum Gratiani: ``The bread which you withhold belongs to the hungry; the clothing you shut away, to the naked; and the money you buy in the earth is the redemption and freedom of the penniless.

That's ST II-II, q 68, art 7, trans by Dawson.