But again strangechild, you've ignored the question. If we didn't deal with him like this then how? The families of his victims may have wanted him alive, ideally, but that could only be done by putting more people in line for exactly the same fate their relatives had, or maybe worse.
We can't negotiate with them the way you can with the IRA or even people like Hamas, because they do not have specific aims or grievances aside from wanting a worldwide extremist Caliphate.
And if through traditional warfare, that would involve far more civilian deaths, destruction, famine and abuse than one targeted strike.
Look at what happened in Europe after WW2, the allies had to fight right the way across mainland Europe from both sides before they got to the Nazi leadership in Berlin. That fighting led to famine, there were mass rapes, children were forced into fighting, people's homes, livelihoods and crops were destroyed.
Yet if we went back to the 1940s and we miraculously found technology which would allow us to pinpoint the whereabouts of Hitler, Himmler, Hess, Goering, Goebbels and Von Ribbentrop and destroy them, vastly curtailing the war and preventing a lot of that destruction, people like you would be wringing your hands over their right to a fair trial and trying to block it.
Yes, the ideal is a fair trial. In reality that's often just not possible, and the alternative is to allow a lot more innocent people to be harmed.
And yes, as I've said before, these people to you are just some faceless, shapeless, rightless mass, because you only ascribe rights to those who have done wrong, not the innocent.