Will leaving Afghanistan be the judicious thing to do today? If yes, why? If no, why not?

My answer is no. The reason is that we should open unconditional negotiations with the Taliban. It's going to be hard to negotiate with all troops out today. It's going to take several months to get them out, anyway.

Now, is it likely that the US will support such negotiations? Not now. Might be if there's a completely different team in charge in 2009.

Until then, serve out the remaining missions, but do not extend them.

After negotiations have lead to a deal between the Northern Alliance and the Taliban, NATO should withdraw. Perhaps there should be a UN-led peacekeeping force, though it is hard to see what it could do. In any way, it should not comprise too many NATO countries, and none of the ones currently fighting.