I'm not sure what your mental model is for someone's visual likeness.
I'd propose a blind-inclusive analogy of what is happening on Twitter is anyone can create a realistic sexdoll with the same face and body proportions as any user online.
Doesn't that feel gross, even if the sexdoll's genitalia wouldn't match the real person's?
My point is that nobody is getting undressed and no privacy violation is being done. Fake nudes are fake.
I knew when this issue hit the fan that you'd get hordes of overly-literal engineer types arguing that the person wasn't actually violated, or that "how is this any different from someone drawing a hyper-realistic picture of someone naked?" I can actually even (well, somewhat anyway) sort of understand this viewpoint. But if you want to die on this hill, you will, most people in the real world would condemn and ostracize you for this viewpoint.
But to your main point: if you agree it's gross, do you not agree it is a violation of _something_? What is that thing if not privacy?
Dignity. Albeit indignation always ends up being controversial in some sense.