Uriel_Hayabusa said:
but from what I remember being Japanese has never been a big part of Shredder's character.
Oh, how wrong you are, being Japanese has been THE biggest thing about the Shredder and Splinter's master/owner/etc. when he was still just an everyday rat. The whole Shredder plot in the comics, first movie, and the cartoons has always come back to it being a big clan war more than anything. Comics, Splinter's master killed Shredder's older brother over a woman, which resulted in him dropping out of school(I forget the exact details, but this is basically what happens) and becoming a ninja to avenge his death. Movie, same thing happened, but Splinter ripped half his face off after killing his master, so he's got a score to settle with the rat. Cartoon, Splinter IS his master (in other incarnations) and Shredder doesn't much care for someone he screwed over still being alive.
His whole backstory is honestly very generic nowadays(though it's normally that of a protagonist), but him being Japanese and their somewhat fictional culture has been a driving force for him from the beginning. That's why fans were pissed off, he's a character that doesn't necessarily have to be Japanese to work, because we know there's a dozen other characters that are about the same, but if you're going to bring up The Shredder, it's probably best to keep him as a guy from that island country East of mainland Asia.