That argument only makes sense if you had a relatively precise idea (up to a factor of 3-5 at least) of how many concerts equate to inhaling second-hand e-cig e

That argument only makes sense if you had a relatively precise idea (up to a factor of 3-5 at least) of how many concerts equate to inhaling second-hand e-cig exhaust, health-wise. Which you don't, at all.