Quite frankly the costs that the US has paid are a tiny fraction of the costs it has inflicted upon the Iraqi people with its staggeringly short-sighted invasion. It can damn well stay until the problem is fixed.
I find it frustrating that most discussions of US foreign policy eventually come down to people complaining that we interfere too much in foreign politics and simultaneously complaining that we should really do more in foreign politics. Let's talk about Iraq for a moment. Here's my entire experience with the Iraq war, as pertaining to me specifically.
Shortly after starting second grade, the World Trade Center was attacked and my school was closed for a few days. I heard a bit about the invasion of Afghanistan but I didn't really understand it. I was quite aware
why the invasion happened though, since I remembered the tragedy that happened in New York. (Hearing that 3,000 people died was pretty devastating to a kid that just experienced the first death of a close family member; my grandmother died a week prior.)
Two years later, America invaded Iraq. This one I wasn't quite sure about, but I figured it was an extension of the other war. I was 8 years old or so, and I didn't know what a WMD was. I occasionally watched coverage of the invasion with my dad. I remember watching a broadcast of the dark sky over Baghdad, my dad told me the army was bombing it. He mentioned that there were a lot of anti-aircraft defenses, and that's what some of the bright flashes were on our TV.
Fast forward eight-ish years, over the course of which our economy's taken a bit of a tumble and we've spent an insane amount of money on the war. I wasn't old enough to vote in 2008, but if I could I would have supported Obama in no small part because I wanted our wars to end. Several people I knew were sent overseas, as well as the relatives of some of my friends. By this point I've run audio equipment and set up for two separate funerals for citizens of my tiny town at the church across the street from my house, including one for the son of my mom's co-worker.
And then, hooray, we're finally pulling out of Iraq. Just about every other country had withdrawn from Iraq, and the country was in a reasonably stable state. We fucked up a bit, but we tried pretty hard to get everything working again. Iraq had a reasonably functional military of its own. I don't have to run any more funerals, we're not spending absurd amounts of money on that war, and my friend's dad gets to come home.
Now that ISIS is going crazy over there, the same international community that left Iraq, and encouraged us to leave (I remember reading Newsweek articles about this!) is asking us to go back. I can't say I have any desire for the US to send troops there again. One of my high school friends is stationed on a ship in the eastern Mediterranean, and I hope that's as close as he ever goes.
Yes, the US fucked up a bit in Iraq. But it's a pretty tall order to just demand some other country send its people off to war just because we've done it before. I don't think that's very fair. I don't know where you're from, but how would you like it if people from another country were asking your friends, your extended family, and your local electronics store owner to go to war in Iraq? That's a pretty absurd thing to say.