Marvin, you raise a valid point. There may indeed be a rational and well formed reason why this take on The Shredder is White rather than Japanese. However, your counter-argument only further higlights the acrimony and irony of the situation.
When possibe explanations are offered in regards to changing Johnny Storm into a Black male, the rancor does not cease. If Sue and Johhny are biological siblings, people say it is perposterous (despite scientific evidence posted in this thread). If people bring up the adoption angle, people call it stupid. Worse, the dismissiveness that people express for blended families displays a level of unfathomable bigotry, as if adopted and step siblings are no less family. How judgmental and offensive!
Conversely, any rational offered for a White Shredder is taken as reasonable. Even though the Shredder is the most iconic and well known TMNT villain (he is the ony villain to appear in every franchise incarnation), he is labeled as tertiary. LaughingMage literally suggested that changing Shredder's race doesn't matter because the character isn't as "important." But why is it that a prominent figure in TMNT, that happens to be Asian, is denounced as secondary? Shredder is the impetus for the formation of the Turtles, so his importance is cemented in the lore.
So yes, it is true that a good reason may be offered for changing Shredder's race. And the reactions to that notion are in line with my earlier comments about the wilingness to have a "wait and see" approach with a White Shredder in juxtpositon with the "no reason is good enough" approch to Johhny Storm. We once again the same problem with people being hypocrites.