As to
vaping publicly outdoors no regulation is necessary. There have been no demonstrable second-hand vapor effects reported in experiments indoors and the greater air quantity outdoors makes something that was negligable to start with almost untracable. In fact in regards to the public outdoors I'm more concerned about inhaling car exhaust and factory pollution than even someone else's second hand
tobacco smoke.
As to long term health effects: Any person who would say that any activity is risk free is naive. Life is full of risk. Risks are taken when crossing a street, drinking a beverage, eating a food item and yes while
vaping. However, I must point out that I strongly disagree with the view that "harm reduction" is nothing more than spin. In fact harm reduction is used every day. We have seatbelt laws because seat belts reduce the harm caused to a person when they are in an automobile accident. We have helmet laws for motorcycles and bicycles because a person riding one of those devices could fall off and get a serious head injury without one. We require a whole host of other devices, practices and etc to reduce the harms and risks of everyday activities. Harm reduction is real, and most importantly it works.
With regard to PVs (I refuse to call them e-cigarettes they are nothing like a cigarette) I would say that any health risks that may be associated with them in the long term are greatly less than continuing to smoke, for which we know the long term risks.
As to the contention that they contain "chemicals" so does everything else. I happen to be enjoying a very lovely bottle of an industrial solvent now, this solvent is called dihydrogen oxide. Given enough time it is known to be able to dissolve just about anything, it is used in waste water treatment, industrial processes, is present in food, and yes too much of it can even kill you.
My point is that just because something is a "chemical" does not make it inherently dangerous when used properly.