You seriously need to scrub up on your history.
Couple of years prior to the 9/11/01, the Taliban executed Iranian diplomats and journalists in a meeting which it had invited them to attend to for "peaceful" purposes. Iran was all geared up to go to war with them after that, but the US Goverment implored them not to (in secret, of course).
Irony:
1. If Iran proceeded, they would have saved the USA from 9/11, as Al Queda would have been busy aiding the Taliban.
&
2. We would be touting the war as an example of that mythical Iranian terrorism.
&
3. The intel Iran gathered to use for the invasion was later given by them to the US, saving months of preparation on the info front. A year after Bush thanked them by calling them part of the "Axis of Evil."
Pakistan has since sought to use the Taliban as its proxy. Seems odd since the Taliban and most of Pakistan is is Sunni and Iran is primarily Shiite, although ethnically the Afganis and Pakis are mostly Iranic ethnicities.
Pakistan had given the Taliban safe haven, and that turned into a problem for it some years ago as they started taking over provnces they were living in, forcing the military to engage in ops to remove them.
Bin Laden was holed up in Pakistan a couple of months after the war started and we knew it. Bush ignored intel when he was still holed up in Tora Bora.
The reason for carrying on the war (other than to benefit the industrial military complex) was the lesson learned since the withdrawel of Soviet troops in 1989 - that leaving a torn apart non-functioning country in the midst of a civil war in the center of the crossroads of Planet friggin Earth is not to anyone's benefit. Establishing gov't, forming and training a military and police, infrastructure, rebuilding society, protecting women, children, and minorities, preventing the Taliban, Al Queda, and other Mujadeen, etc, outfits from taking over.
Leaving Pakistan, Russia, and China the responsibilty to deal with anything is just as dangerously naive as the rest of what you spouted, as their goals are solely framed by what is best suited to exploiting for themselves. It had been suggested that Iran, if anything, should lead the way, given that their hybrid theological/democracy is the optimal model for Afganistan since it already leans that way and as mentioned before, they share enthnic and historical ties. Iran, of course, is a bit worrisome itself and no way our bosses in Israel would permit us to consider anything of the sort.