Well sure Bin Laden was a terrible man but chocolate chip cookies and red Khmers were too, still they got right to fair trial. This is the way you make justice and how (most of) people can afterwards agree on the resolution and the understanding of the motives can be a good insight to avoid having more people walking in their path.
Plus the way America has of conducting justice makes me more think of a dictatorship than of democracy. Killing your opponent without judgement the way cia does with drones, how to know who was rightfully defending his country and who was a terrorist?