There have been a number of these stories lately -- the Daily Mail has mentioned most of them, I think -- and it's been kind of frustrating to watch. The problem is that behind the easy-to-satirise over-reactions there is a serious message. Society, in general, has not been particularly good at acknowledging or even caring about how other people might react to the majority's actions. Now, the people who in the past would have had to put up and shut up don't have to any more.
And yes, like I said, there is a legitimate complaint. It depends largely on your motivations, but it's not uncommon that a subtext of dressing up in the "fancy dress" of another culture would be something along the lines of "look at me, look at how stupid I look", and if for some people the exact same outfit is a matter of tradition and pride, that is pretty disrespectful. If, on the other hand, you were thinking "look at these wonderful clothes, I'm wearing them because of how wonderful they are", then there is, or should be, no offence caused. I would venture to suggest that for most people at this party, they had in mind something closer to the latter.
Anyway, it seems just common courtesy to be aware of other people, and how they might feel about what you say and do. Also, with respect to cultural icons, and what people have said and done in the past, we shouldn't be so eager to view our ancestors through rose-tinted lenses while portraying everyone else as complete ***. Whether or not that means knocking down memorials to them I wouldn't care to say -- it depends on the specific case, right? -- but, again, people have to acknowledge that symbolism is powerful.
I don't think these two themes -- more respect for others, and a more honest appraisal of the past -- are that unreasonable, and these are at the heart of what the current movement is about. Are some in that movement going too far, or getting too aggressive? Very possibly, yes -- the Daily Mail hasn't included in its article a link to a recent story about students wanting a statue of Queen Victoria to be removed, and when I saw that in the Times a couple of days back I stopped what I was doing for a minute or two out of amazement. What I'd ask people reacting to these stories to do is not to let the excesses of the movement detract from the more sensible parts of it.