Someone who sees a bonerack and says "I want to be like them!" has an eating disorder (less than 2% of teens are anorexic). We can go after the ads to protect this segment of the population, but ads don't turn healthy people into malnourished skin bags, because healthy people view it as disgusting and unhealthy.
Consider that being dangerously underweight is almost unheard of in modern society outside of eating disorders, but obesity is extremely common and getting worse (over 22% of teens, according to the CDC).
Even the NIH makes almost no mention of being underweight as being a problem in any age group, and they also show a disturbing trend in obesity, even among kids and teens. (SOURCE)
In my opinion, these ads create the same level of harm for someone who is obese, sees a body positivity ad that normalizes obesity, and says "See, I'm perfect the way I am!", and continues with unhealthy lifestyle choices because of that (as the studies suggest).
Look, I'm bias, I hate ads. I would love to see all forms of harmful ads being banned. Including promoting undereating, overeating, gambling, driving cars, drinking, smoking, weed, religion, and medication.
Ads are designed to manipulate people, and they are especially dangerous when they target vulnerable demographics (like teenage women or the obese), so laws should be put in place to protect people. In addition, I encourage everyone to preserve their mental health and defend against these marketing companies by blocking any and all ads.