[Evil Al]

I think some people tend to think that using a nuclear weapon is more immoral that explosives is because the atom bomb was invented as a weapon of peace. "If we all can't live in peace, then we shall all die."
There is also the problem with the fall out and the long-term damage to the planet. Reducing this would mean that someone would have to invent a cold fusion bomb. So far this have proved to be impossible.
Of course I think using weapons that will kill a lot of civvies is wrong. In war only the military should be targeted. But you could argue that countries start losing power when its people get blown up.