Okay, so first we had to go in to Iraq to stop the monster Hussein from using WMDs on puppies and little Susie.
Then we had to stay in Iraq so the Iraqis would know how gloriously free they were. Of course, we couldn't let them, you know, vote, until we were sure they'd understand how free they were.
Then we "freed" them, just in time for the 2004 elections, and hoped that the American people wouldn't put two and two together. (Mission accomplished!) Still, even though the Iraqis were now free, the Army had to stay. You know. To keep them free.
So we had to stay even longer, because the Iraqis needed to put together a provisional government, then a constitution, then a government, and of course the American government was in no way choosing winners and losers, but just in case the Army needed to stay.
Then the army needed to stay, because Iraq was so unstable dontcha know, why if Uncle Sam left there might be a Civil War. Or worse yet, religious sectarian violence. Note that this wasn't a reason to not invade in the first place, just a reason to not leave now that we're there.
Now that US soldiers are in the middle of a civil war/religious sectarian violence, we need to stay because if they left it might get worse.
Sorry, no. The US should never have invaded. Having invaded, the US shouldn't have stayed as long. Having stayed too long, the US needs to leave, now. Things can always get worse, and they probably will, but the American Army no longer has the ability to prevent said worseness. So anyone advocating a longer - or more numerous - American presence in Iraq needs to STFU right now, and stop talking until the troops are home.