I think if ingredients were disclosed that, first, harmful ingredients would be reduced or eliminated by the makers, and next the public could debate the issue

I think if ingredients were disclosed that, first, harmful ingredients would be reduced or eliminated by the makers, and next the public could debate the issue of banning indoor e-cigs from a position of knowledge. If every product had to disclose this, then ideally you could recursively query for every component chemical. At that point, not only would banning e-cigs be discussed but also probably many building materials and cleaning products. And we'd be able to ban on a granular level, e.g., any product emitting more than 10 ppm diacetyl.