"The best argument for fighting in Afghanistan is powerful and similar to the one for fighting in Iraq: credibility. The abandonment of either country will create a powerful tool in the Islamic world for jihadists to argue that the United States is a weak power. Withdrawal from either place without a degree of political success could destabilize other regimes that cooperate with the United States. Given that, staying in either country has little to do with strategy and everything to do with the perception of simply being there.
The best argument against fighting in either country is equally persuasive. The jihadists are right: The United States has neither the interest nor forces for long-term engagements in these countries. American interests go far beyond the Islamic world, and there are many present (to say nothing of future) threats from outside the region that require forces. Overcommitment in any one area of interest at the expense of others could be even more disastrous than the consequences of withdrawal."