The burden of proof, in this case, should be on the e-cigarette industry. They are selling an addictive recreational product, consisting of a new combination of substances, with a novel delivery method (that involves deep inhalation). It would be naive to let them play the game the cigarette industry has played for decades, that is trying to dodge the burden of proof for safety and spreading uncertainty.

And let's not forget that, for a novel product, the baseline for safety is not using the product, not using something that is known to be extremely toxic.

#1: they're addictive. It's in my list of harmful things