There is a way the United States can win in Afghanistan. There actually is a way. The solution is to refer to Afghanis as "Sioux" and refer to one of our generals as "Sherman." This would be a bad thing to do.
It is always risky to give ideas to statists. No matter how absurd or sarcastic the idea, there is a danger they will take it seriously and try to implement it as policy. For instance, every time the subject of raising the minimum wage comes up, someone suggests raising minimum wage an absurd amount. After all, if the current minimum wage isn’t considered a "livable wage," raising it by 50¢ per hour will not transform the minimum wage into a "livable wage."
In 2001, the city of Santa Monica took the suggestion seriously and tried to set the minimum wage for that city at more than double the national minimum wage and 68% higher than the state minimum wage.
The most successful invasion of Afghanistan was by Genghis Khan. He slaughtered all warriors, sent all artisans out of country back to Mongola, massacred the population, and the young women and children were given to his soldiers as slaves.
There is a reason that kind of war will not be waged. In spite of the subservience of the mainstream media in not reporting atrocities, waging a war of extermination on that scale would be too hard to hide. The United States, under Bush and Obama, already has a horrible international reputation, and it could not endure the international condemnation that would be the result of such an activity. Waging war on that scale would finally mobilize the world to stop the United States, and finally end the United State Empire.
For the United States, this would be a very bad idea. It would destroy any remaining illusion about what the United States have become. But it could be done because the United States do have experience waging this kind of war. Just ask General Sherman or the Sioux.