Into the murky stew of rationales for fighting on in Afghanistan,  Joe Klein throws this ingredient:

we have a moral obligation to the Afghan people, just as we had to the Iraqis when we stomped in there and destroyed the most basic institutions of civil society

Really? America was attacked by people who were given safe harbor by Afghanistan's government. Our retaliation was well within the bounds of international conduct, as opposed to George W. Bush's extremely debatable war of choice in Iraq. It also did not involve the vast infrastructural damage that we inflicted on Iraq. (Primitive and endlessly war-torn Afghanistan just doesn't have that much infrastructure to destrory.)

But even if we concede Klein his point, it feels dangerously open-ended. How far beyond the past nearly-eight years does that obligation extend? What, exactly, do we owe the Afghans? And how many of them are willing to be killed as collateral combat damage while we strive to meet that goal? I think America should do more for the Afghan people, who helped us outlast the Soviet Union and whose future sympathies we want for all sorts of reasons. But I'm not sure that moral obligation should be a central foundation for a continued military campaign there.