In general private/public, commenting on physical characteristics is bad etiquette (or worse).
With public figures, entertainers, etc., it comes with the territory, and clearly this person made the choice to make this an issue on-air.
It's not theory, in the general population it's a fact. A fact. A fact. Which is of course how they rationalize it away, by denying it.
Habits, choice, working around ones genetics and preferences, shifting a diet and gradually aquiring healthier taste, things things take work, and some people avoid it. We all rationalize away the things we don't want to do to some degree. For some, this becomes basically a mental condition, a hardcore refusal to admit reality (and it's not just overeating, lots of people do this with lots of behaviors).
The issue here is that liberals want me, involuntarily, to pay for this persons healthcare. And if I have no choice in that, why the **** should you be free to overeat and not exercise, knowing this will cost me more? Chaining them to me (by me providing healthcare money for them) might seem like a good idea, until I drag them with me at a pace they can't keep up with. Then what, we'll have to restrict my freedom to require them to live moderately healthy if I'm paying their way? Surely this is reasonable!