The problem is not that simple, of course. Yeah, the Taliban would have their hands full trying to 'govern' their country, but the fact is they WON'T. Which is what caused, or rather allowed, the rise of terrorists. Due to the utter lawlessness of Afghanistan, terrorists have a safe haven for planning, training, whatever. Oh yeah, and when they run out of money, they can terrorize the locals into submission, taking the opium crop, whatever.

We have a vested interest in making Afghanistan safe, because it has been a breeding ground for people who intend to do harm to the West. The local population has no real ability to defend themselves from the scumbags who terrorize them. Worse, the terrorists hide behind religion as an excuse for their actions, but the fact is they are thugs and criminals, no different from the Mexican drug gangs or our own organized crime syndicates.

On the other hand, I absolutely agree that imposing a government upon Afghans is a non-starter. The country is (in)famously non-governable, and all attempts have ended in failure. The real question is, how do we prevent an un-governed Afghanistan from exporting its miscreants around the globe? Sure, if they want to allow scumbags to operate within their borders, it's nothing to us, but those same scumbags have traveled all over the world, with disastrous consequences. We cannot allow that, but there does not seem any clear way to prevent it without imposing some kind of government. Upon a populace unused to, and likely incapable of, being governed.