The revolutions in Arab Africa (and simmering in the Middle East) have undermined the goals and methods of Al Queda (this NY Times article is but the latest that has said this)..
And so it is time to get the hell out of Afghanistan. Being an occupier is the greatest threat to people now - regardless of how noble or valid the reason (look at Israel for proof of that). There is no valid reason to stay anymore. Get the hell out now.