I've seen this argument on several MN threads recently as well as other places, but I don't think it fits the facts.
Gay men can definitely be sexist but this particular argument (that gay male designers design for slim androgynous women because they want models to look like young men and don't care about impacts like anorexia) doesn't fit the evidence imo.
Gay male designers have obviously been prominent in fashion but I don't think there's a clear pattern of them designing only androgynous slim women, nor that they secretly want their models to look like men.
If you look at fashion history, the 1920s slim, androgynous gamine look was popularised by the flapper subculture and designers like Coco Chanel. The similar look in the 60s (Twiggy etc) doesn't seem to have been only popularised by gay male designers.
There's also a clear pattern of gay male designers designing for very curvaceous women. Dior's New Look in the 50s, obviously. Then in the 80s,
Versace, Dolce & Gabbana didn’t emphasise androgynous looks, models like Naomi Campbell, Cindy Crawford etc were not exactly androgynous!
Another example would be Gia Carangi. She wasn’t androgynous physically (though in her private life she was more so) and she was supported & promoted by gay men.
The 90s heroin chic era was the one which caused eating disorders : afaik 1920s & 1960s trends did not do this. But was this masterminded by gay male designers? I'm unconvinced. Kate Moss' look fit the grunge-era rebellion against flamboyant 80s looks, it seems more like extreme trend cycling and pendulum swinging to me.
Anna Wintour (Vogue), Isabella Blow, and other influential editors also share the blame for unhealthy standards promoted.
Fashion editors, critics, and journalists — esp magazines like Vogue, Elle, Harper’s Bazaar — were largely women. So we're models, clearly. I think male designers who promote unhealthy looks should be blamed, but so should journalists, editors & models.
This argument also seems to assume that gay male designers want the models to look like the object of their desire (ie. Men). But plenty of designers, male and female, can admire a model' look or wish to emulate it rather than want the model to look more like the kind of person they're attracted to. And if gay male designers, according to this theory, want to design for young men, why would they work in womenswear?