Propylene glycol, vegetable glycerine, food grade flavourings and nicotine, if you have nicotine (you can buy nicotine-free liquids). So, considering all of these ingredients can be found in food, with the exception of nicotine, I wouldn't be too concerned that they are more dangerous than smoking, simply because it's illogical to think that. Yes, vaping is a relatively new thing, but they now have to comply with the EU regulations for TPD (tobacco products directive), which means you can't now simply make your own and sell them to whoever. Sure, you can make your own, but you aren't allowed to sell them to the general public without having them tested and that assurance they are safe.
They also now come with the reassurance that you can check the mods and stuff online at the manufacturer's websites to ensure you haven't purchased a potentially dangerous fake. I'm sure you have heard of some batteries blowing up? Yes, this is why. Because you used to find them anywhere, unregulated and dangerous, which now you can check against to ensure they are genuine. I haven't had any issues with mine, except for my Smok Alien 220 Mod deciding to give up the ghost yesterday which I'm less than impressed with, but at least it simply stopped working and didn't explode...
Also, the 'great plumes of vapour' you describe really depend on what you are using and the type of liquid you use. Higher VG liquids tend to create a lot more vapour, nice clouds indeed if you are into that. Lower VG, equal VG/PG ratios produce less vapour. I used to use 50/50 VG/PG liquids but since swapping to higher end liquids (because I find the flavours nicer and more intense) these are 70/30 or 80/20 VG/PG, which means I do produce more clouds BUT this also depends on how you vape as well. You find people who vape mouth-to-lung and direct lung vapers, directly vaping to lung creates more vapour because you are inhaling more vapour and longer vapes at a time, whereas the other kind (which is me) you are drawing into your mouth first, then to lungs, which produces less of a cloud because you can't inhale as much that way. My husband vapes direct to lung and creates much more sizeable clouds than I do.
The vapour exhaled doesn't contain any nicotine and actually isn't anymore dangerous than inhaling steam from the bath, for those who may be within the vicinity of the cloud. So yes, it may have a smell, but it isn't dangerous.
There was a very interesting documentary about the comparison between vaping and smoking a little while ago which showed the cells in the lungs and what happened to them whilst smoking and vaping, and the difference was immense. This showed, very clearly, that the cells of the lungs in the smoker weren't able to repair themselves. They timed them the same at the same time and what you saw were the cells trying to repair and meet in the middle again, which didn't happen for the smoker, leaving a gap. In the vaper, you could see the cells repairing and meeting in the middle in the same timeframe. The cells of the vaper weren't any different to someone who didn't vape or smoke.
Also there's just the very basic logic of the fact cigarettes contain thousands of chemicals, formaldehyde for one, which are known carcinogens, which will damage your lungs without a doubt. Liquids for vaping just don't contain those things. The only toxic ingredient they do contain is nicotine, only if you choose a nicotine liquid, and this doesn't have quite the same effect. It's highly addictive, yes, but it isn't really the thing responsible for damaging your lungs. It's all the other chemicals that are mostly responsible for the damage.
I would imagine that vaping whilst pregnant, if a 0% nic liquid, isn't harmful. I don't know how much of the nicotine in a liquid with nicotine would potentially pass over to the foetus, but it would be unethical to test this out, obviously. Having said that, when you are pregnant and smoking, what's the first thing the midwife does? Refers you on to the smoking cessation (right word?) midwife. What do they do? Offer you NRT (nicotine replacement therapy), which will consist of patches, gum, spray or that little pipe thing. All of which contain nicotine. All of which pass into your bloodstream, which then, I would assume, passes over to the foetus. This then, isn't any different to vaping. In fact, vaping is now currently used as another form of NRT. So, this would show the NHS approve it for this purpose. Therefore, vaping is most definitely a LOT safer than smoking in pregnancy.
In an ideal world, you would quit before pregnancy, or quit cold turkey, but some people want a little help because some struggle more than others