Because it is. As you yourself allude to later...
> I don't think we should view fatness as a moral failing
It clearly is not. I suspect the only people who believe that are the folks 'born on third base' as it were.
> some people need a bit of a push to kick bad habits like overeating
Some people? The vast majority of people are overweight. Anyone who isn't fit & trim has no business commenting on anyone else's bad habits and moral failings. None. Got a little bit of a spare tire? Shush. Got some love handles? Shush. Skinny fat? Shush again!
> if we can reduce it, we should
100% agree.
Edit: Downvote all you want, guys, most of you pushing that downvote button need to lose weight just as much as I do.