I know people aren’t supposed to draw parallels to Vietnam, but the fact of the matter is the Taliban have a lot of popular support (often more than the central government). They also don’t require much to field fighters, and have nothing but time on their hands (and on their side). What it would take to beat them nobody would ever allow our troops to do. The fact is that in much of the countryside the Taliban move freely, and the central government is only propped up by our troops; it has little authority, and has negotiated with the Taliban (even threatened to side with them) because it understands they have a role there.
The Afghani’s kicked Taliban Ass and it was not that long ago. The Afghani’s hate Karzai, they know he is corrupt to the core. They of course roam freely because if they can’t they make a statement by killing villagers. And as for Karzai to threaten to allow them as part of the government was all for him retaining power. Remove him and put a strong leader in there and the tide will turn.