If you take the logic behind the liberal view of transgenderism and apply it to women with anorexia, then what they really are is fat women trapped in skinny women's bodies. Calling it a mental illness or saying that they should be "helped" makes you an ignorant bigot. Just because you weigh 60 pounds doesn't mean that you can't see yourself as fat. OMG, so much this, its 2015, I can't even.
The same logic also has some interesting implications regarding guys that think they're Napoleon, or Jesus.