While the United States hasn't yet addressed the safety and efficacy of e-smoking, other governments and health agencies have and they always counter us with this:
You have approved, legal, safe alternatives to cigarette smoking with nicotine replacement therapy products already on the market.
That point was driven home in this study in the summary box about what this study adds to our knowledge:
Pharmaceutical grade nicotine replacement products are far safer than
tobacco products, while novel
tobacco products have uncertain risk profiles.
The important words are
Pharmaceutical grade nicotine replacement products.
E-smoking is not in that league. Not at all pharmaceutical, with all that implies and assures. Instead, we use unregulated, poisonous liquid made by companies we don't inspect, selling plastic vials or glass containers without labels, ingredient lists, warnings or child protection. Our devices have one real purpose: Deliver an addictive chemical to an addict, with the possibility of addicting non-smokers by a new delivery method of a substance said as addictive as ...... or ........ It's not a natural plant like tobacco. It's a chemically obtained drug. Nicotine doesn't exist in the wild. It's not natural.
Anyone who thinks we'll just take a high road to eternal e-smoking is smoking something besides PG and nic. Approvals won't come easily, if at all.