You make some good points. I would dispute your last paragraph especially, though. How can Israel, for instance, create a workable balance with its regional enemies when those enemies are irrational and developing nukes? Imagine Iran without a US presence in Iraq and Afghansitan currently.
Also, one cannot forget that during the Cold War not only did we contain from a military/strategic standpoint, but we also contained an idealogy — or perhaps more accurately — we introduced and buttressed freedom in regions that previously had not had it, and in so doing developed long term allies.
And even Iran has positive effects they can provide us. They are no friends of al-Qaeda and the Taliban and they are a whole lot closer to Afghanistan than we are.