Jonah: The answer to your question, in two words (three? whatever), is:
Raison d’etat.
The precise nagging objection that so many conservatives have with
international free trade is that, taken to its logical conclusion, it seems
to require the abolition of the nation-state. This is indisputably true if
you throw free movement of peoples into the mix, as many modern free-traders
do.
That may be a good thing, or it may be a bad thing, but a conservative
thing, it ain’t. Not unless I have conservatism all wrong.