It isn't a moral question, and it is unfortunate that people frame it this way. It is a tactical question - is it worth the cost to bomb civilians, or is that effort better spent bombing strategic targets? Germany took a low cost approach and bombed a lot of civilians. In Japan the cost to the US was very low and fire bombing civilians was very effective (as far as bombs go.) In Europe the costs were higher due to AAA and enemy fighters, and the strategies diverged.

I don't think the Americans were trying to be "moral", but they were trying to get the greatest effect for the effort. The bombing missions were very costly and also very inaccurate at taking out strategic targets.