maybe not an 'evil' euphemism (though it may become so in its usage); but I have never been content with the term 'community', when referring to a demographic.
It suggests that such members of a 'community' are in close contact with one another, care and support one another. I suppose it comes from marxist conflict theory; a community is a group of persons [who identify, or are identifed as marginalised] who hold solidarity to a cause and will express representation in the public sphere.
Again, I feel this is a subtle euphemism.
Yes, that is part of the general falsification of language, that everything shall be called what it is not, or the meaning of a word twisted far from the original understanding.
I think you are right that it IS euphemistic in the sense that it takes people united only by a characteristic or ideology, and implies a greater sense of unity - that of the community as people who actually live together, in the same local geographical sphere - than actually exists. Thus we could speak of a "science fiction community", a "barber community", or "cleft lip community", to show the absurdity of speaking of "the black community", "the deaf community", etc., as they actually do. It makes them sound more unified than they actually are, most often for political purposes.