IMO, many of the anti-smoking crowd who are virulently anti-vaping as well are that way because they thought they would eliminate tobacco smoking through advocacy, shaming and legislation, but they are starting to realize that this isn't how things are going to play out, and that tobacco smoking will largely be replaced by vaping instead.
There also seems to be a sort of "judgement bleed-over" from the idea that smoking cigarettes is not only a risky and irresponsible behavior, but a moral failing on the part of the individual as well. Since vaping looks like smoking and is enjoyable, they react to it the same way viscerally.