Tried the 'grab them by the balls and the hearts and minds will follow' in Vietnam, it didn't work. As I said, if you do shit like that, you sully the moral aspect of the war you're fighting, and hand over legitimacy to the Taliban, as you're conforming to a perception of always oppressing Afghans/Muslims. At least with a democratically elected leader, you can fall back on them being somewhat legitimately elected, as opposed to the Taliban leadership. That's a bigger moral advantage over them than just installing some dictator.
As for the permanent presence, we're talking around 10,000 troops at most, most of whom will be training the Afghan Army (Which is being bankrolled by the US) it's hardly something which is unmanageable.