That seems like a foolish argument. The time horizon in which we discovered smoking was bad for you was decades, and over a massive population of users.

E-Cigarettes are only now becoming mainstream, and have only been in use for the better half of a decade.

We wont truly know the effects until we have a large sample size over a long period of time.

Ultimately, saying it's conclusively better for you than smoking is short sighted. We thought smoking was good for you in the 1920s...