I hate fancy dress anyway, but there's nothing pernicious about dressing up as an American Indian and a saucy Pilgrim, surely. I would have thought that appropriation - the adoption of sartorial mores as a way of life - was a very different thing to fancy dress?
Without wanting to come across all Pete Hitchens, what's really wrong here?
http://www.bbc.co.uk/news/entertainment-arts-37821989