The normal response to this line of reasoning is that they were / could have been doing the same to us. Two wrongs does not make a right does it?
What is the qualitative difference between the killing 100,000 Japanese civilians in one morning using an atomic bomb and the killing 100,000 Japanese civilians in one night using explosive and incendiary devices?
[0] https://en.wikipedia.org/wiki/Bombing_of_Tokyo_(10_March_194...
What does "civilian" mean when it comes to Imperial Japan?
* https://www.nationalww2museum.org/war/articles/there-are-no-...
The official Japanese plan to defend against a US landing was to have children attack the invading US soldiers:
* https://www.hiroshimapeacemedia.jp/?p=141048
* https://apjjf.org/mark-ealey/1689/article
* https://en.wikipedia.org/wiki/Operation_Downfall#Operation_K...
Many more people were saved by dropping the bombs than people died in it. And, while it is a tragedy that those people died, that fault lies with Japan, not the US.