The attack on the world trade centre was a crime, cold blooded murder.
Breaking into someone's house and killing an unarmed man is murder.
He should have been arrested and brought to trial.
It is important to have a difference between the "terrorists" and the civilised, and the difference is law and justice.
That is why it is wrong to torture, imprison without trial, shoot unarmed people, etc...
Killing him raises the question of what he would have said in an open court, after all he was a creation of the west.
Osama Bin Laden and Zbigniew Brzezinski
President Jimmy Carter's National Security Advisor, Zbigniew Brzezinski visiting Osama Bin Laden, in training with the Pakistan Army