Is having a fit body unattractive? Why are people so mean?

I know that health and fitness has to do with more than just weight, and weight isn't always an indicator of health, but why do so many fat people always claim that thin people are starving themselves? I have a fast metabolism, but I eat healthy and don't have any disorders. Yet people, mostly larger women, feel the need to comment on how I eat so much but stay small, and make jokes about bullimia (Which i don't find funny. Besides, I'm not deathly skinny, my BMI is 18.9, I have a , I have ). Why is it that it's wrong to say mean things about fat people, but the skinny people somehow deserve it? I have hurtful, spiteful, meanspirited things said to me for things I can't control, but it's somehow ok because I'm skinny.