Looking over this thread (and especially the first post), I get the feeling that the reasoning behind why foreign policy is important is being missed.

When one country makes others upset, this breeds a resentment that leads the resentful countries to form alliances against the superpower, (usually taking on a military form) to bring it down. This is called "hard balancing" and it brought down Napoleonic France and Nazi Germany.

The US isn't that much of an international threat, of course, and this has led to an international tendency that the media has dubbed "soft balancing". No, Europe won't invade us, but they can still hurt us, in the wallet. They can pay for oil in Euros, not in dollars. They can open up trade with countries that the US has turned its back on. They can exclude the US altogether from trade agreements. They can construct nuclear reactors, and allow them to be constructed in Iran and elsewhere that the US might balk at.

When enough of them get together, they will be powerful, and form a powerful coalition that the US won't be able to laugh off. We can't ignore this, and saying that the only opinions that matter about our policies are within our borders is naive.