Do not agree with LKY on this.
If US withdraws from Afghanistan, the Mullah Omar/Bin laden are ready to take over again.
If that happens imagine the loss of credibility and how Bin laden will be viewed in moslem world.
Maybe after the top leadership of Taliban, Al Qaeda is caught and killed USA can withdraw from Afghanistan.
Otherwise, Pakistan, Iran, China will do anything to resurrect pre 9/11 afghanistan..