The first question one must always ask is "What are our National Interests?"
The Washington Post ran this quote from John Nagle on 31 August:
President of the Center for a New American Security
America has vital national security interests in Afghanistan that make fighting there necessary. The key objectives of the campaign are preventing Afghanistan from again serving as a sanctuary for terrorists with global reach and ensuring that it does not become the catalyst for a broader regional security meltdown. Afghanistan also serves as a base from which the United States attacks al-Qaeda forces inside Pakistan and thus assists in the broader campaign against that terrorist organization -- one that we clearly must win.
U.S. policymakers must, of course, weigh all actions against America's global interests and the possible opportunity costs. In Afghanistan and Pakistan, low-cost strategies do not have an encouraging record of success. U.S. efforts to secure Afghanistan on the cheap after 2001 led it to support local strongmen whose actions alienated the population and thereby enabled the Taliban to reestablish itself as an insurgent force. Drone attacks, although efficient eliminators of Taliban and al-Qaeda leaders, have not prevented extremist forces from spreading and threatening to undermine both Afghanistan and Pakistan. The so-called "light footprint" option has failed to secure U.S. objectives; as the Obama administration and the U.S. military leadership have recognized, it is well past time for a more comprehensive approach.
In a well-stated countering perspective, Major Jeremy Kotkin published the following piece here in the SWJ that argues in fact that we have no such National Interests at stake. Though Jeremy is a bit of a protégé' of mine, and a co-worker here in the Strategy Division at USSOCOM, these thoughts are his own. Jeremy makes a good case, and it is one grounded in sound history as well as the principles of Strategy and Insurgency. Frankly, Dr. Nagl's argument has no such foundation to rest upon.
For your consideration: U.S. National Interests and Afghanistan; and the young, untested Major Kotkin vs. the CNAS machine and Dr. Nagl