Don't want to add fuel to this debate, but what you say sounds a bit strange to me. I am of thin build- slightly underweight- and never felt this gave me any problem. Granted, it's just how my body works so it's possible that if I had to make an effort to keep this weight this would come with some slight issues. On the other hand it's also not normal for a lot of people to be overweight, this has clearly to do with culture and food rather than innate needs. So it's strange that your body would give you negative symptoms for just keeping a natural weight.
So I think the dynamic here is that it's really common to consider women who are of a healthy natural weight to be overweight. I'm not out here defending women who are 5'7" and 200 lbs as healthy but what happens is that that 5'7" woman will be viewed overweight at 150, chubby at 140, and "normal" at 130. And may god help you if you're close to 160. Which is fine for folks who's natural resting weight is 130 but for everyone else it sucks, you end up fighting your body 24/7 to keep it that way and having to ignore/suppress your bodies natural signals.
It's no one person or group's fault that this happens but it's where we're at. I'm technically not underweight by the numbers but my body violently disagrees with that, I've learned to accept it. One of the most common experiences for women in late 20's early 30's is to ease off the constant dieting, gain 10-20 lbs because that's where their body always wanted them, and suddenly feel great -- more energy, less brain fog, regular periods, and suddenly it's not work to maintain it.
Yes, these numbers make the discussion a bit more concrete. But 5'7'' and 150 is definitely in the healthy weight range- girls can strive to be thinner than that but it's to fit some arbitrary idea of beauty rather than to, as you say, "be treated better in each aspect of life" (yes of course, attractive people in general are treated better- but it should be a negligible effect for the ranges we're talking about). In other words, I assumed that the user you were talking to was talking about much higher BMI indexes than these. Personally, as a male, I don't find the 5'7''/ 150 unattractive at all- though it also depends on how fit someone is.
