Foreign policy should reflect international realities, which change over time. The Republic of Korea was vulnerable to renewed North Korean aggression at the conclusion of the Korean War in 1953. Today, Seoul could do whatever was necessary to deter and defeat the Democratic People's Republic of Korea. There's no need for America to defend that which could be defended otherwise.
I'm not so naïve or recalcitrant as to deny the fact that the surest way to wreck the American economy -- to take it from whatever point it sits at today and send it straight into the abyss -- is for us consumers to voluntarily go on a six-month austerity kick, a period during which we don't buy anything except stuff we actually "need."