They were not killing japs for politicians. Ever hear of Pearl Harbor or how the Empire of Japan tried to take over the western world. Marines have one purpose and one purpose only; To Eradicate The Enemy with Extreme Prejudice. Sure they brainwash you is a matter of speaking but, you wouldnt expect someone with normal ideals to perform the acts of heroism and honor as real Marines do.
Semper Fidelis
No one is besmirching the honor of the Corps but the average trigger puller on both sides was conscripted, young and fighting a caricature of what they thought the enemy was. For sure Pearl was a big factor for the Marines but there is still humanity there. I think it was the second episode where they find a journal and picture on a dead Japanese guy. That is what I would have a problem with, knowing that without the war I was no different than the guy laying dead on the ground next to me. I can't say for sure because I have never been in combat but I could do my job when it needed to get done, find a target, line up, slow squeeze, next target...but I know for sure it would bother me later.
All that being said I don't know that I would have issues killing Taliban. Every single one of them is willing to pick up a gun so that girls can't go to school, music is banned and apostates executed. Same goes for criminals, you are making a conscious choice to harm me or my family and left me no other option (I am a point and shoot guy, not a point and "stop mister or else im gunna shoot!" guy).
I have a cousin who is a Marine and has done multiple tours in A-stan and Iraq. He is Mr. Macho all the time, judges his manhood by how many girls he fucks (hes married with a kid on the way) and how much he can drink. Before one of his deployments he came over to my place, we split a case of beer and I watched him cry about the shit he had done and seen. Marines are the toughest SOB's out there but the PTSD and suicide numbers don't lie, war effects them just as much as everyone else.