In our war with jihadis we must compromise our ideals. Saudi Arabia produces too much oil to attack or even pressure too much over their support for extremist Islamic training. Pakistan is too important to fighting in Afghanistan to push too much over their failure to crack down on their side of the border and perhaps even flush out Osama. Their nukes make it even harder since we don't want to provoke an Islamic revolt in Pakistan that gives jihadis a ready-made nuclear arsenal.
One of the benefits of overthrowing the mullah regime in Iran and replacing it with a government that reflects the pro-American sentiment of the people of Iran will be the land corridor it will open to Afghanistan.
Now, our access to Afghanistan is from the north through the unstable "Stans" and back through an increasingly unfriendly Russia; or through Pakistan which we have to coddle to keep land-locked Afghanistan from being cut off from us.
Open up a supply route through Iran to Afghanistan and suddenly we don't need to be quite so reliant on our Central Asian bases or so careful with a Pakistan that will not crack down on the Taliban who hide and organize inside Pakistan. We won't have to be so shy when it comes to hunting bin Laden there, either.
I want Pakistan to defeat their jihadis and remain a friend of ours. But we are in a tough position because of Afghanistan's geography in pushing Pakistan toward a normal existence free of jihadi influence. Reduce Pakistan's importance in fighting in Afghanistan and they have less leverage to resist our pressure to reform and crack down on the fanatics.
Free Iran from the rule of the mullahs and our freedom of action in the region expands greatly.