The hubbub around Boston's Museum of Fine Arts was particularly distressing, mostly because the protesters completely ignored what the Japanese (as you said) and Japanese-Americans had to say about the matter. This article gives a pretty good run down of the issue, I think. Importantly, it notes that the kimono isn't really standard ware in Japan, so people perhaps don't necessarily associate it with Japanese culture in the same way that people in India still see the sari, for example.

I mean, that's not to say that there aren't problems with cultural appropriation in certain places - the UK has a few 'holi' festivals that really boil down to a bunch of drunk rich kids running around throwing colors at each other, and I definitely take issue with that, but yeah, protesting wearing the kimono is a tad strange when the Japanese have historically been pretty OK with that. Especially when you consider that there are many, many other Orientalist aspects through which we look at Japanese culture that people often just outright ignore.