If we could fully satisfy our economic needs, it would be theoretically fine for us to ignore exports and just focus on our internal market. However, there are some goods we have to import, either because they’re inputs we don’t own much of (e.g. some rare earths), because other countries have a comparative advantage at producing them (German cars), or because we could produce them but like the imported versions (Scottish… Scotch?).

Having a comparative advantage at consumption only works if we also have a comparative advantage at selling assets, since that’s the other half of the formula. But the financial assets we sell are ultimately claims on the real goods we produce.

Finally, there’s the market discipline aspect. It’s easier to sell something domestically than internationally: Americans use dollars, speak English, and we’re all right here. By selling goods internationally, we double-check that we’re not just producing stuff that’s convenient, but stuff that’s world-class. And if you walk through the implications of traditional Ricardian trade theory plus the fact that we’re one of the world’s richer countries, the implication is that we should have at least some exports we’re world-class at.