And let's address the immediate point as well, shall we?
With the Saddam regime deposed, just WHO is the enemy at this point? The Sunnis, most of whom are fleeing into Syria and Jordan, or the groups we've enabled as the de facto rulers of the country, the Shi'ite militias allied with Iran? That is our problem: an escalation of the war against al-Sadr and others only further isolates that bunch we call the Iraqi government, holed up behind a mile of barricades inside Baghdad.
Now, the issue is:
(A) honoring our word to the Kurds, et al, who trusted us, (if for no other reason, so that other will trust us in the future);
(B) not allowing Iraq to become a chaos s-hole like Somalia and/or Afganistan, which breeds jihadis; and
(C) not allowing Iran to take over Iraq, which it would do if we let things run the course.
But Ron Paul's and Jack Murtha's cut-n-run approach is not the answer.