You know, I never thought of it that way. You might have a good point there. Whatever animosity exists between Sunni and Shia (see the sectarian violence in Iraq for instance) it does seem that they have no problem uniting against their common enemies: the US and Israel.
I'm afraid you might also be right about the necessity of dealing with Iran. I'll admit the prospect of a war with the Iranians (and possibly at the same time Syria) is not a prospect I look forward to. I'm not saying the US and Israeli militarys would not prevail, but it would be REAL ugly. Unfortunately, it looks like we're on a collision course with just such a scenario.
You know, the burning question is, and it has been asked by Rush Limbaugh just a couple of weeks ago, "do we want to fight the Iranians before or after they have nuclear weapons?" Because war with Iran is a question of when not if.
I have made the point repeatedly on this site that Iran has been at war with us since the fanatical shia coup of 1979. The problem for us, is that they have been aggressive and we have been on the receiving end. They violated international law by allowing the "students" (Mahmoud the Mad was one of them) to seize our embassy in Teheran. They sacked the place like the Huns sacked Baghdad in the 1200's. They incarcerated and tortured our embassy staff for 444 days. They were instrumental in providing the support to the hezzies to kill over 200 Marines in Beirut back in 1983. There are many more examples of incidents which in my mind provide for a casus belli.
In sum the West cannot allow a terrorist state such as Iran, actually the epicenter of world terrorism, to acquire nuclear weapons. A messianic martyr complex with nukes is a dangerous thing.