First thing: you’re basically just assuming I’m not Japanese. Which I am not, but anyways it’s still inconsiderate.
I used Japanese as an example, I could have used
any cultural clothing at all and my argument wouldn't have changed.
You probably don’t like when stereotypes are made about your own country, so why are you saying its okay to do that?
I'll start off by stating that I'm British, and I
seriously don't care about stereotypes about my culture; not one of them, not the one where Americans think we have weird teeth, not the one where other cultures think our dishes are unpalatable, not the one where people think we're uptight, tea-crazed loons; we find the stereotypes just as funny, if not moreso, than the people who came up with them.
An American person could dress up as a
Queen's Guard and I wouldn't care, like at all, even if they erroneously called themselves a "beefeater" (which is similar, but not the same thing).
Think of it this way. T-Shirts were invented in America, and could therefore be considered a part of American culture, would you deny someone from another country the ability to wear a T-shirt? Equally, Tuxedos were originally a British thing, would it be right for British people to say other countries can't wear them because we came up with them first?
With the Sheik thing, there are more layers to it than just "pretending to be a Sheikah", she's also honoring her (possibly deceased) mother figure by wearing the garb of her people.
One can wear the clothing of another culture while still respecting that culture, and just because someone wears a costume, that doesn't make the portrayal inherently disrespectful.