1) We didn't get to vote on it the first time.
and
2) Hell no. It wasn't necessary at all.
I'd gladly risk the lives of "x amount of troops" over targeting "y amount of civilians and troops", even if I somehow had magical proof that X was bigger than Y. Civilians were not expendable. Targeting them should be a war crime, or a crime against humanity.
If we can have the moral high ground using the nuke, then why can't Al-Qaeda get the moral high ground in 9/11? We've already established that we're comfortable with targeting hundreds of thousands of civilians. We'd already killed nearly 200,000 (all civilians) in Tokyo with regular bombs. In Hiroshima we took out between 90,000 and 140,000 by the end of the year. We had a general saying we didn't need to use the nuke because he personally "had already bombed Japan back into the stone age." They were done for. It was just a fucking fatality move for style points.
We fucked up. We made a mistake.
Japan was out of food and ammo. They were sending Japanese troops out with just a couple bullets, and sometimes none, telling them "you can just kill a stupid American and steal his gun." These soldiers were starving. And the kamikazes were forced into it. Nobody wanted to die. We could've just sieged them and starved them and been done with it.
The only reason we dropped the bombs was because we were mad that the USSR met us halfway through Germany. We wanted to show off our new technology to scare the USSR and the rest of the world, flexing our power, and showing that we took out Japan without the Soviets' help.
And we'd narrowed it down to 12 or so cities to bomb, and we bombed the rest of the country. But not those 12. We wanted those cities to be really nice, so we can get some good before and after pictures. We decided the time and date, but not the city. Then that morning, we picked Hiroshima, because there wasn't a cloud in the sky, so we'd have nice weather for our photographs. We finally donated those photographs to Japan a couple decades later, and they're in the Hiroshima Peace Memorial Museum. They're insane.
Also, the Japanese got an assload of documentary film footage from the days immediately after the bomb, and the American occupation ordered it destroyed and wouldn't let anybody research the effects. We realized how evil and horrible it was, and we were ashamed of it, and tried to cover it up. But somebody hid some of the footage, and it finally resurfaced in the 90's. It's pretty fucked up.