Only Al-Quaeda, Iran or radical Shiites like Al-Sadr would benefit from a civil war. The Sunnis would get creamed and they know it. They don't like it, but they see it.
EVERYONE would get creamed and they finally figured that out. The Shiia who want an independent state are minions of Iran. The "independent state" would exist for all of a week before it was taken over by Iran. The Sunni would be almost wiped out before the surrounding Sunni states could step in, the Kurds would be walled off in the north to forever watch their pipelines blown to bits, their vision of a thriving economy go up in smoke as the rest of Iraq faced years of chaos.
No, it would be ugly for all of them and most Iraqis have figured that out.