Are there any studies on whether widespread social disapproval of smoking has reduced the smoking rate?

I'm not sure of any specific studies, but I'm sure they been done. I would say that this disapproval can have the reverse effect. Reactance, which is an emotional reaction in response to rules that eliminate or threaten behavioral freedom, probably occurs. Reactance is the principle of "reverse psychology"-- that is, telling someone they can't or shouldn't do something often has the reverse intended effect and causes them to want to do that.