Bring out the Holy Hand Grenade of St. Antioch!
Call me cynical, but I really believe this is the authentic chain of "reasoning" that leads to discussions like this:
America still suffers from its Puritan roots and views any vices as an affront to God. Therefore, anything that benefits sinners or the "morally weak" by mitigating the negative impact of those vices must be a bad thing. By allowing sinners to avoid the risk of cancer without suffering, we are helping them to avoid their just punishment at the hands of an angry God. Vaping allows the sinner to avoid the risk of cancer without suffering the pains of withdrawal, therefore vaping is wrong and must be outlawed. In order to do this, we need to pretend to have a rational reason (separation of church and state, you know), so we'll dig up or manufacture any cockamamie set of "facts" we can find to support the decision that we already believe is the morally correct one. Then, we can do exactly what we were planning to do all along, in the "scientifically proven best interests" of the people.
Currently, we're in the "fact finding" phase, because the FDA hasn't been able to dig up enough cockamamie facts to support the decision they want us to come to yet. But, it's only a matter of time.
The fact that poor people smoke more than rich people, and that vaping therefore helps poor people more than it helps rich people is just gravy. After all, if God loves someone, they wouldn't be poor in the first place.