On WWII-era Japan being worse than the CSA
You're totally right, but quoting Rummel is a bad idea IMO - he's kind of a nut.
On WWII-era Japan being worse than the CSA
The former part is right. The slavery happened along the way, but was never as extensive as it was in the South, nor a core aim of imperial expansion. At least AFAIK. Theirs also a the fact that being conscripted into forced labour during a war is less morally repulsive(at least to me, and I expect to most people) then permanent plantation slavery.
Anyway your initial point was that the Japanese empire was worse then the CSA. Nothing you've said has justified that assertion.
If there is no Holocaust of Jews, there are still Nazi atrocities against Slavs & other groups :/
Slaughter of civilians by soldiers contrary to official policy<starting a civil war to guarantee that almost half your population remains enslaved. At the very worst those war crimes were a means to an end for the Japanese government, whereas slavery was the end for the CSA.
Also, the CSA states had, in living memory, engaged in similar or worse war crimes against Native Americans(as had many Northern states).