“Healthy at any size” is a reasonable stance, and one in reaction to a medical system and social norm of being mean and hateful towards overweight people. BMI is not the only measure of health, but doctors will regularly tell heavyset patients with real other diseases to lose weight.

Fat people are literally the only group where it’s just OK to make fun of them, in many circles.

Even for those who are overweight and unhealthy, berating and shaming someone is never going to be a way to help someone heal.