I think you're absolutely right that at least for some of them it probably is some kind of mental health disorder. However, you don't see the guy on the bridge ready to jump saying "You're oppressing me, suicide is healthy". Anorexics try to hide their behavior and, while it's a very difficult process for them to get better, you don't see them saying "I was so much healthier when I was 85 lbs #haes". So the real difference for me is that other people, when confronted with the possibility of their mental illness, reflect and realize they need help. The obese just keep trying to get bigger and get triggered if you dare say "the O word" to them.