I raised this question in relation to Iraq and the Surge in January 2007. Sam Roggeveen applies it to Afghanistan, with perhaps even better effect:
The moral argument for remaining in Iraq in 2006-2007 was much stronger, since the ethno-sectarian violence taking place there at the time, though not caused by the U.S. invasion or presence, was unleashed by the removal of the Saddam Hussein regime that had effectively stifled it (or rather, monopolized it through one-sided, state-sponsored brutality).
Afghanistan, on the other hand, was already in the midst of a civil war when we invaded. There is the added element of reprisals against Afghans who cooperated with U.S. and Coalition forces should we now leave. But the case for the West being morally responsible for the violent divisions in the Afghan state is far less compelling, or else it dates back further than the current war. And even if there is a case for it, it is certainly not reduceable to the American unilateral use of force, given the broad multilateral support for the initial invasion (as evidenced by the vigorous debate now going on in Australia).
So to take Sam’s thought experiment one step further, imagine that if instead of invading Afghanistan in 2001, we’d managed to destroy al-Qaida’s base structure and safe haven there through precision air and missile strikes, with the same result of displacing AQ to the Pakistani FATA. What about the current situation in Afghanistan would argue for the introduction of a massive U.S. and allied military presence there, as opposed to military assistance to Afghan opposition forces of the sort that effectively defeated the brutal Soviet occupation in the 1980s?
And if the answer to that question is that we could accomplish whatever is realistically possible in Afghanistan indirectly through Afghan proxies, what about that answer is inconsistent with beginning a responsibly paced drawdown now?