The war is not black and white; good versus evil. Almost nothing in the world is that simple and straightforward. Do you honestly think it would become a great place to live if the US just withdrew?
This is not a competition to count up who did more worse stuff. We as a country have been caught in a slippery slope with no easy completely morally correct way out. The fact is that we are in the war now and playing monday morning quarter back does nothing.
I'm sure that our country didn't think their actions of having americans in saudi arabia would have pissed off Osama and the countless other hijackers bad enough that they attacked us on 9/11. But the fact is they did, then the Taliban provided safe haven for them and our only option to try to avoid similar attacks in the future was to go in and get rid of the safe haven. If we leave now, the taliban will take over and it will be a safe haven again. If we stay, our fellow americans continue to die in an ugly horrible war.
Where was the easy right morally correct answer in any of that that was readily apparent at the time?