You confused your personal morality, which seems more based on "would this rule benefit everyone applied universally" with the question you were asked, which is of the "does this provide the greatest good to the greatest amount of people" variety.
It's _possible_ that in the end, ecigs are not a net positive for humanity. But that is a belief without firm proof. They could be twice as addictive, but if they kill only 1/3 of us that cigs did, they'll be a net benefit. And 1/3 the lethality of cigarettes seems to be a drastic overestimation of their harm from the evidence we have right now.