We also didn't put FDR in prison for the misery he caused the Germans or Japanese. I don't recall FDR asking their permission to invade or bomb them. And we didn't put Truman into prison for the misery he caused the Koreans. FDR's actions killed more innocent civilians than the Iraq War did. That's not whataboutism or misdirection, I plainly dislike Bush & Co., they're all monsters. The US should not have invaded Iraq, it wasn't in the US self-interest to do so, it was a wildly irrational choice. And yet the context is a lot more complex than you're suggesting.
Saddam is gone. Iraq is a fledgling democracy, which was unthinkable 25 years ago, and their oil output is persistently near record highs.
Iraq has a GDP per capita higher than Indonesia, the Philippines, Jordan, Egypt. And not far from South Africa or Paraguay. It's not a total disaster at present, they legitimately have a chance to build something there in the coming decades.
These two things are simultaneously true: Iraq's future prospects are better because the US invaded, and the US should not have invaded.
The Korean War involved dramatically more misery than Iraq did. Millions of people died in just a few years. Ask the South Koreans if they would prefer that the Kim family were ruling over them while they exist in absolute poverty today.
Isn't it just fascinating how today nobody dares to proclaim that the US should have left North Korea to conquer and rule South Korea, that that would have been the obvious better outcome vs the misery they went through for decades after the war. No, people wouldn't dare to say that, but they'll say it about Iraq, because it's a convenient stick to beat the US with. If Iraq's fortunes improve in the coming decades, those same people will go largely silent on the matter and the narrative will be modified (go back and read how the narrative on the Korean War changed across the decades as South Korea's situation radically improved).
The people of Iraq have a chance to chart their own course democratically. The US doesn't rule Iraq, we didn't take their oil, we didn't annex their territory. We lost two trillion dollars and thousands of soldiers trying to stop them from killing eachother in a religious war. The situation in Iraq is very far from perfect, so what, the lack of perfection isn't a valid counter argument; the situation in South Korea after the Korean War was very very far from perfect for decades.
Even the US was a basketcase for decades after its founding. It was held together by a string, ultimately culminating in a very bloody civil war as well.
It took decades for South Korea to build up the structures necessary to sustain itself as a democracy and lift the standard of living of its people. They were still poor as recently as the early 1980s. Why is it that people think Iraq should have been instantly transformed into a mecca? That's a level of expectation nobody would dare apply to any other similar context. As though the end of Saddam's rule was somehow going to be soft and fluffy, rather than involving misery. There was no other scenario than to go through misery given the sectarian split in Iraq and the way Iraq was being ruled, it was always going to prompt a civil war.
The issue is that the US was involved. It's an easy point that can be used to hit the US with.
How can I be sure of that? Well, simple, consider the alternative. The opposite position is: condemn the people of Iraq to living under Saddam and his sadistic family (or the equivalent). I'll note that was a minority political group oppressing and torturing a far larger majority group through a brutal totalitarian system with zero human rights. Condemn the Iraqi people to go back to that? I'd challenge someone to dare to say that right now and then back it up as the better alternative to the present (that's not what would happen of course; a person will instead proclaim a fantasy scenario of fluffy bunnies and utopia where glorious happiness and peace would shine from the sky magically and all the conflicting groups in Iraq would hold a love-in and Saddam would have just willingly retired as dictator-for-life and then there would have been no civil war in the aftermath and instead it would have been an organic gentle process).
I'd like to see someone stand up and proclaim it would have been better if the US hadn't rescued South Korea from being enslaved by North Korea's Kim Dynasty. Because that's exactly what people so often openly proclaim about the Iraq situation, including its majority Shia and minority Kurds who were brutalized by Saddam.
The US shouldn't have gotten involved in Iraq, it should have never invaded Iraq. However the prospects for the people of Iraq are not worse today than they were under Saddam's reign of terror. And it's entirely an intellectual con that Iraq was supposedly stable under Saddam (one of the few arguments frequently thrown out in support of the Saddam scenario). Iraq was extraordinarily unstable under Saddam, which is why he had to constantly murder and purge people. When you have actual stability you don't have to slaughter and torture people; Saddam had to do that constantly to prevent his system from collapsing due to its inherent instability.