Okay, here is a scenario that I will probably get a lot of shit for, but maybe it will give you some perspective on your position. Osama is a muslim leader. The actions of the US have greatly harmed his people (support of Israel, economic influences in the Middle East, military occupation, supporting oppressive regimes, etc.) Those were people who had never done anything to Bush (or another president.) What if, instead of flying planes into the World Trade Center, he assassinated Bush? What if he lit him on fire and watched him burn to death? How could you say that is wrong, if you are willing to do the same to Osama for killing innocent people?
Another scenario: An Iraqi's family is all killed by the US military. They were not insurgents, they were just in the wrong place at the wrong time. According to you, it would be totally justifiable for that person to torture Bush to his heart's content.
I AM NOT SAYING IT IS OKAY FOR THESE PEOPLE TO ASSASSINATE THE PRESIDENT. I AM NOT JUSTIFYING THE WORLD TRADE CENTER BOMBINGS, THE KILLING OF IRAQIS, US ACTIONS IN THE MIDDLE EAST, OR ANYTHING ALONG THOSE LINES. IF YOU SAY I AM, I WILL IGNORE YOU.