The thing is, its not nicotine which is the prime cause of health problems with conventional cigarettes, its the by-product of burning vegetable matter and particularly of the preservatives that exist in 'ready-made's' . That which gets described over-simplisticly as 'tar' and is basically the condensed by-products of the smoke that you have sucked deep into your lungs.
I've been assured both by a (non-smoking) chemist (that is, a senior man in chemistry, not a pharmacist) and an ex-employee of the tobacco industry (before e-cigarettes had been thought of) that smoking joints is just as dangerous, or very nearly as dangerous, to health as smoking roll-ups, It's the smoke, basically, bringing the toxic tar deep into the lungs, not the 'active ingredient'.
So on health grounds there really is little justification in banning e-cigarettes, in fact it would make more sense to ban normal cigarettes now there is a much less dangerous alternative available. No doubt the government can tax e-cigarettes and that can compensate the state for any remaining health problems so caused.
Having said which, I gave up smoking over 20 years ago when I realised exactly how much damage it was doing to my health, and I don't intend to start again, e-cigarettes or not.