I've been privy to this discourse for over a decade, it seems that a few things are true all at once:
1.) No one should comment on a stranger's weight.
2.) it's ok to point out some weight gain if you're in a close social in-group.
3.) Doctors should take all patient's complaints seriously, regardless of body weight.
4.) Obesity is a public health issue.
5.) having a body with a lot of fat cells, will ultimately reduce your quality of life. Most people, in the affluent, industrialized, West are carrying too much fat on their bodies and becoming leaner can resolve a great deal of minor to moderate chronic conditions.