Continued firebombing (which absolutely would not have stopped, and would've increased in intensity) alone would have killed far more than the bombs did.

Yes. that was the argument put forward. Similar arguments have been put forward for almost every military and major terrorist action ever taken. People can subscribe to the justifications, or not, as they see fit. The real thing to be cautious about is if you accept such justifications but only when your country is the one making them.

Yeah, but the argument put forward for everyone may not have been acceptable to some working on the project.

It is important to note that the physicists working on the gadget came from diverse backgrounds and had wildly different politics and moralities when coming to decide if they should work on what they saw as a doomsday weapon.

I always see it posed as "we either nuked Japan or we invaded", but the nukes were absolutely used in preparation for a land invasion. Nuking Hiroshima and Nagasaki fit into the highly controversial US strategy of strategic bombing Japanese industry prior to a land invasion, and they were not even the most deadly of our strategic bombing campaigns against Japan (the fire bombing of Tokyo was worse). A proper invasion of Japan post introduction of nuclear bombs commanded by one of our most infamously nuke happy commanders, Douglas MacArthur, planned to have US troops marching through the radioactive wasteland formerly known as Japan slaughtering anything that resisted them. It wasn't an either or, we weren't nuking Japan as an alternative to a land invasion, we were nuking them in preparation for a land invasion

They could have dropped the bombs on the coast or a non populated area as a warning, and act if they didn't surrender though. That's a demonstration, dropping it in a city/town was not, that was a masacre.

The usa looked at Nazis and went "wtf only we get to be like that" and thenattacked nuked Japanese civilians