It's sort of like the classic market segmentation problem. Ideally you want to charge each customer the maximum price they're willing to pay, but it's hard to give different prices to different people. Likewise, you want to push each person towards the least harmful version of smoking or non-smoking they'll accept, but you can't tailor general advice like that.

In any case, it seems like much of the e-cig debate comes down to this. Those in favor see it as an alternative to cigarettes for smokers. Those against see it as a way to get non-smokers to consume tobacco.

Or even: get non-smokers to consume over-priced perfumes that have a good profit margin whether or not they contain tobacco/nicotine.

Just this weekend, I saw a friend of mine vape who'd never touched a cigarette. His arguments were "Relax, it ain't a cigarette." and "I only vape for the taste of the liquid."

I expressed skepticism that burning random chemicals and inhaling the resulting smoke is healthy. Good to have some evidence to back that up.