Again, fat person here. Being fat is not healthy, physically or mentally. No we shouldn't attack or criticize people for being fat, but acting like being fat is perfectly fine is wrong. BMI might not be a good system, but that doesn't mean the idea behind it isn't.
“obese” arbitrarily medicalises fatness
Fatness is medical. Fatness comes with a host of health problems. To say it's not medical is some anti-science bullshit.