But I want to add another and less obvious objection: Hussein's mind would have been a unique resource for historical, political and psychological research, a resource that is now forever unavailable to scholars.
Imagine that some science-fiction equivalent of Simon Wiesenthal built a time machine, traveled back to 1945 and returned to the present with a manacled Adolf Hitler. What should we do with him? Execute him? No, a thousand times no. Historians squabbling over exactly what happened in the Third Reich and World War II would never forgive us for destroying the central witness to all the inside stories, and one of the pivotal influences on 20th century history. Psychologists, struggling to understand how an individual human being could be so evil and so devastatingly effective at persuading others to join him, would give their eyeteeth for such a rich research subject.
Kill Hitler? You would have to be mad to do so. Yet that is undoubtedly what we would have done if he hadn't killed himself in 1945. Hussein is not in the same league as Hitler, but, nevertheless, in a small way his execution represents a wanton and vandalistic destruction of important research data.
He should have been locked up, by all means. Kept him in jail for the rest of his life, to be sure. But to execute him was irresponsible. Hussein could have provided irreplaceable help to future historians of the Iran-Iraq war, of the invasion of Kuwait and of the subsequent era of sanctions culminating in the invasion. Uniquely privileged evidence on the American government's enthusiastic arming of Hussein in the 1980s is now snuffed out at the tug of a rope (no doubt to the relief of Donald Rumsfeld and other guilty parties; it is surely no accident that the trial of Hussein neglected those of his crimes that might — no, would — have implicated them).
Political scientists of the future, studying the processes by which unscrupulous leaders arise and take over national institutions, have now lost key evidence forever. But perhaps the most important research in which a living Saddam Hussein could have helped is psychological. Most people can't even come close to understanding how any man could be so cruel as Hitler or Hussein, or how such transparently evil monsters could secure sufficient support to take over an entire country.
What were the formative influences on these men? Was it something in their childhood that turned them bad? In their genes? In their testosterone levels? Could the danger have been nipped in the bud by an alert psychiatrist? How would Hitler or Hussein have responded to a different style of education? We don't have a clear answer to these questions. We need to do the research.
Are there lots of Husseins and lots of Hitlers in every society, with most ending up as football hooligans wrecking trains rather than dictators wrecking countries? If so, what singles out the minority that do come to power? Or were men such as these truly unusual? What can we do to prevent them gaining power in the future? Are there changes we could make to our political institutions that would make it harder for men of Hitler's or Hussein's psychological types to take them over?
These questions are not just academically fascinating but potentially of vital importance for our future. And they cannot be answered by prejudice or preconception or intuitive common sense. The only way to answer them is by research. It is in the nature of research on ruthless national dictators that the sample size is small. Wasn't the judicial destruction of one of the very few research subjects we had — and a prime specimen at that — an act of vandalism?