I don't know why no one else has pointed this out, emp, but the premise of your argument is quite obviously flawed. You begin by stating that you can say people who are underweight/anorexic are unhealthy and look awful, and that "no-one or almost no-one is offended" by such a statement. I counter that we could probably find quite a large number of people who would be offended by your separating underweight and anorexic with a slash, implying that the terms share equal negative conotations, let alone the fact that you think they are unhealthy and awful-looking.
Now, perhaps underweight people are less confrontational than others--less prone to throw their weight around in an argument, if you will--but nonetheless I believe we could still exceed your operational value of "no-one or almost no-one" quite easily, perhaps with a Google search, and thus invalidate the rest of your argument.
QED
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It is an act of faith to assert that our thoughts have any relation to reality at all. - G. K. Chesterton
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