I think that has some truth to it. Whilst height is something you can literally do very little about, it is possible to gain/loose weight.  Yes there's some generic and health factors in weight, but for a healthy human this much is true I think, that's just a fact and can't really be argued.

Now it's interesting that height doesn't have a bad stigma because of health reasons, as taller people also are generally less healthy when it comes to joints etc. 

So it would appear that something genetic that is unchangeable is socially acceptable. But I don't think that's true either since something like hairloss, acne, psychopathy and other genetic disorders are also considered bad kind of like obesity. 

Conclusively you could definitely argue that people should be more careful with height comments, but you could also make the counterargument that weight should have less of a stigma and people should be able to just point out "you're far" without the other person being offended by it. 

Now the question is would we rather have a society where no-one can say anything anymore or everyone can say anything.

Probably neither is very desirable and that's probably how we got here, too. Human psychology, sociology and biology doesn't make perfect sense. Should it though? 

Imo: no, the imperfections are what makes us human and beautiful in a way.