Unlike Joseph, I think social conservatism and economic leftism (if “leftism” means willingness to significantly restrict trade) are very easy to reconcile on the level of philosophy and, outside the US (a nation whose rather counterintuitive but seemingly immutable political categories were conjured by a mage named Ronald Reagan), fairly easy to combine in practice. For instance, Joseph includes the encyclical’s concerns about mobility of labor in a catalog of “left-leaning topics,” but in the context of the encyclical its connection to social conservatism is apparent. Benedict writes : “…uncertainty over working conditions caused by mobility and deregulation, when it becomes endemic, tends to create new forms of psychological instability, giving rise to difficulty in forging coherent life-plans, including that of marriage. ”
Social conservatives want to encourage comprehensive virtue, or, to use the encyclical’s terms, integral human growth. Such growth requires strong commitments to other persons (which usually includes commitments to particular places), the patient cultivation of relationships of love and responsibility. It should be clear how the constant movement of goods and persons (and the constant push to do and have more, and the construal of practically all things as consumer options) under real existing capitalism sometimes threatens communities. Consumer societies incentivize displacement and foster psychological restlessness. To the extent that limiting trade can limit this vicious restlessness, the social conservative has a reason–not, obviously, a decisive one–to push for limits to trade.
None of this is original, so I am genuinely surprised at Joseph’s description of the encyclical. The encyclical may be occasionally wrong, or vague, or naive, or what have you, but I don’t see how it is somehow vacillating or incoherent. Of course it’s quite possible that I simply misunderstood Joseph’s point, so I’d be interested to hear more on the subject.