I believe that number was 1 million casualties, estimated.
Kind of a clincher as to whether to do it or not.
Sympathy was small because of the brutality of that regimes leaders, and their alledged & real atrocity,.. in war and their treatment of prisoners.
Of the over 60,000 allied prisoners who died while in captivity, (beaten, starved, beheaded, from untreated diseases,) the Japanese say 20,000 were killed by allied action.
These numbers will always be up for debate.

"Oh, I don't think they wanted me to talk really, it was just their way of having a bit of Fun. The "Swine"...The trouble is...They make such Bloody-Good Cameras."
Group Captain Lionel Mandrake

Some true, from bombings and the Arisan,Enoura,Shinyo and Oryoku Maru's.
But...
If you read accounts from the survivors of these ships you'll find that as the ships were sinking the Japanese were throwing grenades into the holds, and machine gunning anyone who tried to come out the hatch.
So those numbers are exaggerated to soften the ... well...call it what you will.
There are the medical expieriments, Poison/Biological/Plague etc., as well.
Decisions are hard, and very much subjective.

__________________

Morbius, Morbius! Something is approaching from the Southwest. It is now quite close.