It's definitely a vice. I can't confirm, but I believe smoking fetishists receive just as much criticism (or rather concern trolling), and while the drinking/drunkenness fetish is really niche, if their liver/heart doesn't kill them first, their impaired thinking probably will.
Bonus (negative) points if two or all three apply to someone.
As for health issues in of themselves:
-Underweight women can have trouble becoming pregnant simply because the body can't provide for two. Women are meant to have some degree of fat, though maybe not of this board, hence their breasts.
-Muscle is more dense than fat, so obviously there's some discretion between whether someone is heavy because of their muscles, their fat, or in between. Strongfat master race and all. It's also why the BMI is bullshit because calling a wrestler morbidly obese is probably not a good idea.
-Fat can provide energy and insulation for sickness. Probably comes from the principles of hibernation and how it's done to outlast the cold.
Whether they're a doctor or not everybody's gonna say something different. It's just proof that if it's none of our business asking questions is just causing conflict.