I get the spirit of the original post, and I find myself wondering too. Firstly, with regard to smoking cessation, vaping is the greatest thing since sliced bread. Seriously, I have become a pretty vocal advocate and have been responsible for 10 or more smokers trying it, in the last month. So, I'm totally down with vaping as a means of smoking cessation.
Is it safer than cigs - hell yes! Do I now feel better than I did, when I was on cigs - oh yah. And I entirely sure it's safe - not really. To be honest, there are some morning I wake up with some trouble breathing and a sore throat. But, this needs to be put into perspective, as I know I vaped over 15ml just yesterday.
At a minimum, it's a matter of moderation, and I feel physical symptoms, when I vape too much. Not a matter of VG or PG, it's about whether it's 2ml or 12+ml. At least that's been my experience. Still, I always wake up feeling better than I did, after even one pack of smokes.
The jury is still out for me. I do enjoy vaping, and plan to continue for a while. But I do plan to cut down significantly, at a minimum. That's how I look at it.