Ibn Muqawama (guest poster at Andrew Exum's Abu Muqawama) does an excellent job at summing up the arguments of the two camps in a post made a few days ago. Yeah, it's a few days old, but the hell with it, I was enjoying my R&R leave.
It is important to note (as David Kilcullen did in an article this week) that the war in Afghanistan is useless unless Pakistan is brought into the fold as well. The US campaign of 2001 and 2002, by most accounts, chased the Taliban and al Qaeda across the border into Pakistan. With a population many times that of Afghanistan, plus a small stockpile of nuclear weapons, the Taliban and al Qaeda's presence in Pakistan is increasingly disturbing. Denying safe haven in Afghanistan only caused our enemies to take up residence in another safe haven. (Indeed, al Qaeda seems to be a very mobile organization).