I haven't read the Wikileaks documents, or even much of the summaries of the Wikileaks documents, so I have nothing to say on this except to express the feeling I've had for several years, which is that Afghanistan is neither winnable nor particularly worth winning. I'll try to come up with something more original later. In the meantime, Jim Fallows has actual thoughts:

The Obama Administration policy I most disagree with was his decision late last year to double-down in Afghanistan. Although I am not an expert of Afghanistan, I opposed this choice it because everything I have learned about the world makes me doubt its central logic. That logic is: if we bear down for a limited time, in a limited way, that will make enough difference that we can then begin to leave -- rather than simply preparing to leave now. At first glance, these documents cast severe doubt on the idea that staying for another 18 months -- who knows perhaps another 18 years -- would truly "make the difference" in transforming Afghanistan.

The argument for bearing down is that the dangers of withdrawal are too great to allow any other option -- which of course was also the argument about Vietnam. As a matter of logic, we can recognize two extremes. Some causes are so vital that, even if they seem hopeless, there is no choice but to persevere. Eg: the RAF during the Battle of Britain. On the other extreme, some efforts are so hopeless that, even if they seem vital, there is no choice but to quit. Eg: the Confederacy at Appomattox, the Japanese emperor after the atomic bombs. At any point in between, it's a matter of balancing the hopes of success against the stakes. If "can we do it?" were no concern, it would obviously be better to keep the Taliban out of power and remove one possible base of Al Qaeda operation. But it's not obvious that the answer to "can we do it?" is yes. Indeed most recent news points the other way.