Are you not paying attention? The fact that they invaded for no discernible reason that would benefit the country is the evidence that they did it for personal reasons.
So if you had your way, Saddam Hussein or one of his sons would still be in power in Iraq. I'm sure that would be great for the Iraqi people. Remember that there is a UN estimate that the sanctions imposed on Iraq after the 1991 were killing 30,000 Iraqi civilians per year. I can link to the study if you doubt me. Thus if the U.S. had not invade in 2003 and things had remained as they were an additional 450,000 Iraqi civilians would've died up to this point. Several times more than died in the war and its aftermath. By any reasonable standard the invasion of Iraq was the merciful option.