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The problem is that radical Islamism is a great unifier, so I don't think the "nation" would splinter if we withdrew. It would simply be overrun, much like Iraq was without our support. Withdrawal would come with the price of understanding that Afghanistan would become a safe haven for radical Islam, which has the ultimate goal of forced, violent conversion of all other religions and nations to Islam. That's not a cost I'm comfortable with.

I agree with you. Please understand that from time to time I am prone to overstate my position so people actually read the posting. Nevertheless, we cannot occupy or (insert your word for it here) indefinitely. The administration screwed up in 2003. They underestimated the resiliency of a committed group of guerrilla fighters and changed directions before we had actually won in Afghanistan. Oh they were on the ropes make no mistake, but the politicians of today have a habit of not letting professional soldiers actually finish a war. In so doing, they condemn us to return again and again. Invariably the enemy is far more capable every time we return. We left the job unfinished in Afghanistan and rode off to save the world from Saddam Hussein. Again we kicked their butt big time, but our policy of demobilization of the Bathist elements in the IA (actually demobilization of the entire army) created a very large number of disenchanted and aggravated veterans with no work, no prospects of work, millions of tons of explosives and other weapons, and with enough training to be truly dangerous. From this element arose the resistance that we dealt with until "the Surge" eliminated a lot of the middle management and we continued to capture their top brass. Iraq was a secular Islamic state and religious fervor was never very strong there. Enough of them however were able to be recruited by AQ in Iraq later morphing into ISIS, ISIL, or DAESH (whichever name you prefer). By destroying Iraq the way we did we created a political vacuum and nature hates a void.
Now to the point of all this. That entire area, Iraq, Syria, Afghanistan, (and soon Iran) is a bottomless pit. We cannot continue to fight these people as we have for the last 17 years. We are not the worlds, monitors, policemen, protectors, or any of the other common descriptives. Either we get out of the region and completely overreact to their attacks on the US and her interests, or we just finish it now. Eventually it will come down to that anyway. Right now none of the countries that really can threaten us are not quite strong enough yet. In our "over reaction" they will see a nation with deadly resolve that has had enough (like the greatest generation of WWII). Everyone knows instinctively when the "big guy" has had enough. When the big guy has had enough few sane nations will antagonize us. Insane nations will be dealt with in turn. Remember how the Roman's were described "They make a desert and call it peace". We need to learn that lesson again.