As reported by Marc Ambinder, Obama, in a rundown of alternative courses to the one he's chosen, said:
The other argument is that we can sort of stand pat, whether it's at 30,000 or 40,000 or 50,000, you have some platform there, you're basically pulled back and hunkered down but you're able to prevent Kabul from being overrun; you can still project some counterterrorism operations in the region. The problem there is whether that level is 50 or 60 or 70, you have sort of a flatline, where there is no inflection point, there's no point at which, we can say conditions have changed conditionally sufficiently so that we can start bringing our troops home.
Note the escalation in Obama's presentation of the troop level needed for this "option": 30-40-50-60-70. Perhaps there have been advocates for all those levels. But compare the fully articulated strategy of one dissident from the outlines of the McChrystal plan, Rory Stewart:
The best Afghan policy would be to reduce the number of foreign troops from the current level of 90,000 to far fewer – perhaps 20,000. In that case, two distinct objectives would remain for the international community: development and counter-terrorism. Neither would amount to the building of an Afghan state or winning a counter-insurgency campaign. A reduction in troop numbers and a turn away from state-building should not mean total withdrawal: good projects could continue to be undertaken in electricity, water, irrigation, health, education, agriculture, rural development and in other areas favoured by development agencies. Even a light US presence could continue to allow for aggressive operations against Al Qaeda terrorists, in Afghanistan, who plan to attack the United States. The US has successfully prevent Al Qaeda from re-establishing itself since 2001 (though the result has only been to move bin Laden across the border.). The US military could also (with other forms of assistance) support the Afghan military to prevent the Taliban from seizing a city or taking over the country.
The core of Stewart's argument is that such a commitment would be sustainable -- and calibrated to a realistic time frame for Afghan development:
While, I strongly oppose troop increases, I equally strongly oppose a total flight. We are currently in danger of lurching from troop increases to withdrawal and from engagement to isolation. We are threatening to provide instant electro-shock therapy followed by abandonment. This is the last thing Afghanistan needs. The international community should aim to provide a patient, tolerant long-term relationship with a country as poor and traumatized as Afghanistan. Judging by comparable countries in the developing world (and Afghanistan is very near the bottom of the UN Human Development index), making Afghanistan more stable, prosperous and humane is a project which will take decades. It is a worthwhile project in the long-term for us and for Afghans but we will only be able to sustain our presence if we massively reduce our investment and our ambitions and begin to approach Afghanistan more as we do other poor countries in the developing world. The best way of avoiding the mistakes of the 1980s and 1990s – the familiar cycle of investment and abandonment which most Afghan expect and fear and which have contributed so much to instability and danger - is to husband and conserve our resources, limit our objectives to counter-terrorism and humanitarian assistance and work out how to work with fewer troops and less money over a longer period. In Afghanistan in the long-term, less will be more.The alternative to Obama's surge put forward by Stewart is not, per the argument framed by Obama, maintaining a mid-sized force too small to improve the status quo until we get exhausted. It's to keep a force (and aid effort) that we can maintain for decades to foster a development that will take decades. Stewart might argue (he hasn't) that his strategy is comparable to securing one's financial future with a $1000 yearly term life insurance payment, whereas Obama's is comparable to slapping down six figures in a risky derivative bet.
Obama could argue that Stewart's course is seductive but false: that a Taliban thriving long-term in large parts of Afghanistan will destabilize Pakistan; that with 20,000 troops the U.S. can't sustain intelligence operations; that there's no viable mission for 20,000 troops. Here, he didn't.