I don't vape but I understand why people would.
I think a couple of the main concerns are that:
A) It could be a stepping stone to smoking cigarettes
B) We're unsure what the effects are, as we don't know how the ingredients affect the lungs etc
Ultimately I guess it's up to the companies to provide the information and for a person to make an informed decision as to whether they should take the risk. People enjoy vaping, whether there's a risk or not, but people skydiving, riding motorbikes etc also take the risk as part of the enjoyment, I don't think it's up to us to judge the people who do it!
Hell, I bet sitting in front of a computer screen all day is as dangerous as vaping!