When something is wrong, it is wrong all the time. As much as I dislike the current administration and as much as they are responsible for the illegal war, I have no excuses for the troops either. Every single man or woman fighting in an illegal war shares responsibility, especially since they all are volunteers. There is no compulsory military service in the USA (as it is still in many other countries), so no one is forced to be a soldier. Each and everyone who joined up did so of their own free will, gets paid for it quite well and has no excuse for the crimes they participate in.
After WW-2 we put German and Japanese officers on trial for following orders. Many where executed, many more imprisoned for long periods. When this whole sad affair is over, US officers (and politicians) can expect the same.