This is one of many times we have left a newly emerged democracy over there, without making sure things stabilized. If we leave Iraq, it is far from the first time we have failed the Middle East.
Our own democracy didn't start off right. We were very shake-y. The French had to help us during the Revolutionary (or to the English, the Civil) War. We had wars within ourselves like the Civil War afterwards, but we did have in many cases support and help by countries outside our own.
Setting up a new type of government, even if it is better in the long run and means more freedom for the people at hand, requires a LOT of work, and a lot of help. We've gone in there with a mission of what to set, and if we leave, we're leaving them to the dogs, and we've done that far too often in countries outside our own, even when we were part of the action occurring there.