While using nukes, particularly at the outset, well before you'd have any knowledge whether such a "last resort" weapon was required, would be inadvisable...
the question must be asked: How much darker and more chaotic can the middle east be than today? How do you destabilize a region that has no stability to begin with? How can whatever comes after Sadaam Hussein, or the Ayatollahs, or Assad, or Fahd be any worse than those characters are to begin with?
Even a depopulated middle-east (the darkest of all ages) would be preferrable to the current lineup.
If the US was to nuke Saddam, it could very well open the flood gates and possibly ignite nuclear exchanges between other nations who have nuclear weapons capability, like Pakistan and India. Iraq could then attack Israel with WMD and Israel would retaliate. If you remember your physics, all out nuclear exchanges, would create a nuclear winter effect and throw the world into darkness and chaos.