I think that we can all apply the same respect for human life.
I don't understand how it is that us nuking a civilian population was okay back then... but if say, Iran were to detonate a nuke in New York City right now because they fear that the U.S. is going to attack them, it would be a horrible crime against humanity and an act of terrorism. After all, Iran doesn't have the kind of technology that could be used to take out U.S. military bases with few civilian casualties. The only way they could get the U.S. to back down is to show what Iran can do. And just hitting NYC would be quicker, cheaper, and less deadly than a full-scale attack on the U.S.
Using the same logic, wouldn't it be fair for Iran to hit NYC right now to deter a U.S. attack? What else can they do? It's their only hope!