That's like saying the person who pressed the button to drop the bomb on Hiroshima was only one person.
Yeah, hes one person.
One person who killed 40,000 people.
You could also consider that the gigantic B-29 that dropped the bomb had several people on it, and if one disobeyed the order, the others would still carry it out.
Plus there was the guy giving the order, the guy who told him to give it, all of the people who voted and debated about dropping the bomb, and the scientists who worked on the Manhattan project.