My definition of 'minimalist' government is probably far more minimal than most...
I also believe that virtually anyone who ascends to the Presidency of Afghanistan is going to be tainted much like Karzai. I pointed out to a friend the other day that our politicians are not a great deal better, they just have a few more social constraints.
We are not going to 'fix' Afghanistan; not least because the social constraint process there is quite different and those pertaining to good government we have developed over centuries (heh!) imply time they do not have. However, we did say we would 'fix' it. That was regrettable political hype or abysmal stupidity -- probably a bit of both. We cannot foster the establishment of a decent government there for three reasons; the Afghans don't want one; we don't have the time or money to do that; and the Afghans don't want one...
So we need to acknowledge that reality. Will and Krulak are both correct on the practicalities and all the reasons to say 'we tried' and just depart except for two that neither addressed: We have not really tried thus far. We said to the world that we would not again abandon Afghanistan.
For those reasons, I'm pretty firmly convinced that we should give it a bit longer and really
try to do the 'fix' thing -- my perception is that is in process with State taking ownership of many things they should've had six years ago -- and we need to depart fairly soon, couple of years or so, with the fond blessings of a nominal Afghan government much as we are departing Iraq. That means a continuing but far lower key engagement. My perception is that also is in process (couple more Fuel Tank Trailers may speed that up a bit...

). It'll take a bit.
The COIN view of ten years or more engagement is unlikely (and highly undesirable IMO) and departing abruptly presents many difficulties. A moderate approach between those poles with acknowledgment that Afghan government will be an Afghan construct and thus unpalatable to many in the west.
The alternative, Krulak's Hunter Killer Teams would require probably about 2-300 well trained platoon sized elements, around 10K troops plus about half that for support (X3 to allow for rotation) to decently cover the 936km Iranian border and the 2,430km Paksitani border -- both in some really bad terrain. You could provide fewer but that is really not an economy of force mission if you expect any success at all.
To leave and "go back punitively" is a pipe dream. May work in bong reality but on the ground, there is no infrastructure there to damage and no cohesive force to be punished. IOW, it would be late 2001 all over again. We could easily do it. Then what?
Hopefully we'll have learned from this to avoid such arrant stupidity in the future. We can and should assist the UN and others in nation building; we should assist internal development diplomatically and with USAid -- and even commit police trainers and SF where appropriate -- but we need to realize that commitment of a mass of US Forces will change the dynamics in generally unpredictable but most always adverse ways.