My guess is that the bans on e-cigarettes are due to their effectiveness in helping smokers quit, combined with their tax-free status. The governments of the world pull in billions on tobacco tax revenues.
My understanding is that without the free-based nicotine in most (all?) commercial tobaccos, the addictive nature of smoking is significantly reduced.
Interestingly, one of those friends is now able to smoke socially at will. Flipped some addiction trigger or something. I would love to see a study on this.