Why are we still in Afghanistan?

[NumberSix]

The reason we are here still, is because we knocked the Taliban out of power and destroyed what little infrastructure Afghanistan had. As the world's police and the greatest superpower in the world it is our moral obligation to set them up to try to prevent the Taliban from coming in and taking over as soon as we pull out.

I've read the Afgan government is rife with corruption, I predict if US ever leaves the government will collapse.