I believe that the reason it comes off that way is that the pacific theater was so brutal, the enemy looked different than us, worshiped a different god than us and neither side had any compassion for the other. The PTO is probably the best modern example of mans inhumanity to man. Don't get me wrong ETO was a bad place to be too, just not in the same horrific way as the pacific.
I considered most of that when I was thinking about it last night.
At the end of the day; I think you are correct that, no matter how politically incorrect, the fact that the Japanese "looked different" than us and because their values were different (religion, government, etc) than ours, the PTO is the obvious choice.
My next thought was that any discussion of humanity or brutality in the face of a lack of the former begins and ends with the Holocaust so that dog doesn't hunt.
Perhaps its more our perception of the IJA being populated by fanatically loyal, death > capture types in comparison to the majority of the German soldiers who were "people." I dont think we ever viewed the Japanese as human beings, frankly.
Dunno. It was an interesting question to ponder. Whatever the combination of catalysts, Vietnam fits the same mold and serves as a backdrop for the same basic message: "War = bad... mmmkay?"
The description of the Eastern cultures as "alien" is probably more spot on than we realize.
Even the fallschirmjager in BoB were depicted as fearful. I dont recall any movie/series/show about the PTO wherein any single Japanese soldier, airman or seaman was ever perceived as anything less than a machine.
The scene last night where the Marines were taking pot shots at the guy in the creek? Did you feel an ounce of compassion for him? I didn't. More importantly; no matter how twittleed up that is; I think the point of that scene was to show that they didnt have much compassion for their own lives either. Read: inhuman.