(because it is damaging for society as a whole, and for young people who are developing their self image, to be bombarded with an unhealthy body shape put forward as something to emulate
And this ^^
Who said anybody should emulate it?
There are thousands of other photos on that website, of models with a whole range of body shapes.
There will be young people with a natural body shape similar to this model. Who are you (or the ASA) to tell them that their body shape is "unhealthy"? The ASA have explicitly stated that this model does NOT show any signs of being unhealthy at all.
Should models with small feet modelling shoes be banned because then young women with larger feet might bind their feet? Should models with larger breasts be banned from modelling bras because young women may then get breast implants?
This is utterly ridiculous, to shame a healthy, tall, naturally slim model and publicise articles telling anybody with a natural build like her that their body shape is unhealthy and they look ill and it should not be allowed to be shown unless photographed from an angle that others deem suitably disguises these characteristics so as not to hurt their feelings because their body might be different. FAR more damaging for the ASA to have done this and publicised it and threads like this to exist, than for them to have just left the advert alone.
The hypocrisy of the whole thing and the inability of many posters here to see the logical inconsistency in their position, that somehow they will protect women from harmful damage to their body image by denigrating the natural body shape of other women, is quite astonishing and depressing.