Jiggling is not the problem. You focus too much on the superficial aesthetics. There are kids out there who are normal weight and eat junk most of the time. Maybe they won’t be hitting puberty early but they aren’t healthy either.
People should want to be healthy because it’s better for them and they’ll feel better. It shouldn’t be to LOOK better.
Having said that, people’s self esteem goes up when they think they look better. But if overweight becomes the new norm people won’t think it looks “bad” anymore; it will just be normal.