The thing about Linebacker etc is that the idea was to bomb NORTH Vietnam flat, leaving the South (the allies) alone... and the result when the US did have a go was to drive a political solution forward - ie 'bombing them to the negotiating table'. I think it's rather more debatable whether continued bombing, having destroyed the North's ability to wage war with its conventional forces, would have also caused the VC to fade into the woodwork. Now transfer the idea to Afghanistan - were exactly are the good guys going to live while the regionally identifiable bad guys get the bombs?
It's also somewhat debatable whether bombing Afghnistan flat* constitutes freeing the Afghan people from the shackles of extremists and allows them to take their rightful place amongst developed nations...etc
*I decided 'back to the stone age' was probably not as big a move as it sounded.