I've said this to friends of mine very frequently. Iraq is hard, complicated, but it is potentially a democracy. Afghanistan is not.
As a person who is a supportive admirer of the U.S. military with a good idea of what they're capable of, I say, with all due respect, there is no way we can accomplish our objectives in Afghanistan. They are incredibly well trained and creative fighters with nothing to lose. The terrain is impossible to navigate for non-natives, which they use extremely effectively, since much of it is so rugged. And there is much of it since it is a huge country. Also, the customs are completely foreign comparable almost to nothing else in the world.
There are some people you just leave alone.
Iraq had a history and people who could adapt to modernity because they once were known as Babylon and had a great empire and great history. They are commercially savvy. I also believe Iran could turn around down the road. There's hope there. But Afghanistan is literally like taking a trip to a land out of Lord of the Rings.
I am not a person who is scared of adventure and risk provided there is a potential for reward and some geopolitical benefit that can be derived. But what's the point of going in to Afghanistan? What - Go git Osama? Please! Do they have oil? No. Are they in an important locale? No. Has any foreign Army ever won there? No. America needs to seriously think about what we're doing in Afghanistan.