For many many years I didn't understand why the atomic bomb was considered somehow "worse" than mass firebombing like Tokyo or Dresden.

In the end a friend gave me a good explanation (ironically a Japanese friend who'd attended high school in the US). He said it seemed "unfair" because only one bomb was dropped, while in a mass attack, seemingly much more effort is expended by the attacker and, more importantly, the target has a "chance to fight back" (forget how ineffective anti aircraft fire was in those days, and still is).

After learning that, when this topic came up I would query about where the objections lay and surprisingly, my friend's explanation was quite common -- probably the majority -- even if the person didn't frame it that way.

A disturbing quirk of human nature