I get this all day, every day. Hearts and minds, people, that's what it's about. We're' at war with an ideology sadly, specifically, the "quit or die" approach which is now hammered across so hard that even non-smokers think that is the only option.
For smokers, I usually ask: "if you could get "Marlbro' Zero", that didn't actually kill people- felt the same and allowed them to smoke anywhere, didn't make you smell, and costs a fraction of a pack of your normal cigs, you'd smoke them, right?"
That's what this is...
For non-smokers, I'm content for them to think I'm trying to quit; but for the curious I have a different answer for each question. Most commonly I explain that people lose their lives in house fires mostly from smoke inhalation, right? It's the harmful part- this is vapour- so it doesn't have the harmful effects of smoke.
I nearly always put it this way: "these are for people who love smoking, but don't want to die from it. I have the choice when crossing a road to walk in front of a bus, or behind it, one is very dangerous the other much less so, and I have the same choice with my cigarettes."