I came across this a while back. It seems to me that there are very drastic differences and risks depending on the brand/source of the Vaping liquid. The market is growing and evolving faster than any regulatory agency can keep up with and scientific studies take time to complete.
I think the issue is knowing what is in your liquid. I purchase my liquid, currently, only from one shop that I know uses good materials (USP Food Grade). I am going to start making my own soon... I mean come on it's cheaper and anyone who took the equivalent of high school science class would know how to measure in ml.
If the people your buying the liquid from is using bad ingredients then as a consumer you should have asked questions... it's also why I don't buy it from online vendors.
But I can't really think of what anyone would put in it that is nearly as bad as cigarettes.
There have been studies done on them, as I listed above, that show it's not unsafe to bystanders around unlike cigarettes so I'm a happy vaper. As for my own body... I know I feel better.