Fashion criticism is dangerous. The reigning method seems to be the fashion police format made popular by the late Joan Rivers. The comments come by the second. Each one funnier and more cutting than the last, they prey on the petty racisms, sexisms and ageisms that present themselves as acceptable opinions.
It works as a statement. The revelation of both the buttocks and the breasts at an event where they are not usually seen will more often than not set tongues to wagging. It would have worked better if she'd said that her appearance at the Met Gala was her attempt at bringing the plight of women the world round to the world's attention before the event. If that was the case then she could have come out on the red carpet naked with the words, "Ageism is Bad. I am free to show off my body as I see fit" written across her length and breadth. If she'd done that we would have spoken about the cause she was fighting for and not the way she looked.
It's the same way you phone in to work a good hour before when you know that you're going to be late. When you turn up thirty minutes late with a story, it seems a little bit like an after thought. Be that as it may, she deserves applause for drawing the attention of the universal fashion police from the truly trivial topic of her clothes and placing it quite firmly on a far more deserving cause.