The problem with the killing of dictators, extrajudicially or otherwise, is the empathy those executed can claim from them. Whether it be a mobbed Mussolini hung up like a slaughtered pig on a petrol station, the trapdoor giving way in the middle of Saddam reciting his prayers, an unarmed Osama bin Laden shot in the face, or a pitiful Colonel Gaddafi dragged out of a sewer pipe bathed in blood. These final, individual acts of brutality are a concentration of the inhumanity these individuals and regimes inflicted. They are much different to the cowardice of Hitler's suicide. Any semblance of compassion for them in these undignified fates is contrasted to their psychopathic absence of this morality that they committed en masse. In this we can define a civilized preference to see the forces of totalitarianism in the docks of courts of justice instead.
Take Slobodan Milošević tried by the International Criminal Court: