What would have been the result had we left Germany in 1948?
There was a defined nation state aggressor the Soviet Union which would have with Geopolitical certainty advanced to occupy all of Germany, and much of Western Europe. In our invasion and occupation of Iraq, we became the Soviet Union.
If we had left Iraq one year after our invasion, Hussein would have come out of his hole in the ground and would have consolidated his power again, and Iraq would not be much of a threat to anybody, The United States would have trillions in the bank, and 4k alive Americans.
Under your argument, if it is taken to the logical conclusion, the Germans would have arisen and became aggressors again. It was not the Germans who we occupied who were the threat. It was the Soviet Union. The invasion and occupation of Iraq, like all occupations was an utter failure from it's inception. The war was won in weeks, but it took 10 years of failed policy and a failed occupation before we successfully withdrew and reaped the horrors of the seeds we had planted.