As I just wrote, Islamic radicals need a place to call home, whether we approve of their stunted world view or not.
Of course there’s more to consider, specifically that many Afghan women want U.S. and international troops to stay in the country until their safety and preferred lifestyle is assured.
That’s the thorny ethical problem of leaving Afghanistan in the clutches of the Taliban, the ill effect on the people trapped there under their primitive form of government.
From the U.S. perspective, Afghanistan is different in this regard when compared to Iraq: We broke Iraq and assumed the burden for fixing it, whereas Afghanistan was a failed state when we arrived. As such, questions about whether we are obligated to establish a stable society there are legitimate.