I'm of the opinion that people concerned about body shape discrimination are bothered by the treatment of all body shapes - but those worried about larger body shape discrimination are not worried about smaller body shape discrimination.

Like all the people who go "being overweight is a risk factor for x! and y! and z!" and don't believe you when you tell them all the things that being underweight is a risk factor for (osteoporosis and heart problems and a whole bunch of stuff that I can't remember right now but which you can link back to insufficient nutrition if you really want to).

I spend more time than I am societally comfortable with (I'm comfortable doing it, but I am uncomfortable that the biases of society make it so I have to) reassuring women at dancing that they're gorgeous, and they don't have to try to get down to my weight because I'm trying to gain weight for my health.