Our Black Sheep ally Pakistan is a haven for way too many jihadi terrorist groups:
We could cut the Gordian Knot with a friendly post-mullah Iran that would provide a line of supply to Afghanistan that doesn't go through Pakistan and which gives the Pakistanis leverage to get away with murder.
So many problems in addition to Pakistan would be made better (I won't claim solved) with a non-nutball Iran.
I'm not the only one to see Iran this way.