It is forbidden to say being fat is unhealthy, undesirable or to pathologize it at all.
Does that seem sensible?
But whether it's acceptable to be fat or not, it's ultimately a social measurement that changes like the wind.
Objectively and biologically, being fat is not good for one's health. Period. There is no room for argument here. Being fat is unhealthy. Being too skinny is also unhealthy, incidentally.
The people in america we're talking about can barely walk. They are not just fat, they're morbidly obese.