They didn't claim only the Allies engaged in this behavior, nor that Japan was blameless. Their claim was in the first sentence, and let me quote it verbatim:
> "That type of behavior is a consequence of war. It happens, and the victors define who is worthy of punishment or praise."
And it goes on to elaborate:
> "Because the allies won, those actions are rationalized, and those rationalizations have merit. Had Japan won, events like the rape of Nanking would have been rationalized by their standards, and actions of the US Army Air Forces would have been viewed very differently."
To spell it out, the argument is that it's silly to single out the Haitians when they murdered their oppressors (and people in the same social caste as their oppressors), because this kind of stuff tends to happen in war regardless of who the involved parties are. Western powers engage in it in their own wars and conflicts, it's just that since they are usually considered the victors, this behavior is less often singled out as barbarous (it is, but less often). Conversely, nobody identifies the former Haitian slaves as part of a victorious West -- especially since Haiti is a failed state and decidedly not part of "us" -- and therefore it's easier to single them out as barbarous and genocidal.
Things not claimed in the other post:
- That Japan wasn't guilty of similar crimes.
- That it was just Allied behavior.
- That the US was worse than Japan or viceversa.