While the Iraqi insurgents have, from what I've read, been growing increasingly dissatisfied with what are presumably foreign, though whether they are or not is anyone's guess, groups who are killing Iraqis, the name Salvation Movement sort of gives it away.
I don't think that it has come to this - Iraqis fighting other Iraqis within the insurgency - nor do I think it will ever come to that so long as Iraqi territory is under American occupation, but there are bound to be a few people who buy into this (abroad I mean, not in Iraq).
Mujahideen in the '80s, the Northern Alliance in 2002 and now, in addition to the Kurds, this. Since its a safe assumption that there is no group within Iraq, with the excpetion of the Kurds, that wishes to see the American occupation continue for another day, this basically amounts to arming your enemies.
edit: besides, rumours are that Zarqawi is already dead.
