I think what you will Find is that the Long Term Effects of inhaling PG and VG have been Studied. But Not on the Frequency or Dosages that are seen with the Average e-Cigarette User.
And Nicotine, well, that gets down to Who you Believe?
What the Real Wild Card in the deck is the Flavorings, Colorants and Sweeteners. And the Chemical Interactions when 4 or 5 Flavorings is Combined with an Artificial Sweetener.
Are e-Liquids 100% Safe. I Don't Think so. Are the "Safer" than Smoking Tobaccos? I believe they are.
It was just a statement, I have no bias either way. I'm one of the few whose reasons for switching had nothing to do with my health. (Although I am of the opinion that it is better, even long term.)
Regarding those studies about PG & VG, I honestly don't think they have any bearing on vaping. As you said, the amounts are so far different, I just don't think it's applicable. I would relate it to a study on the safety of working at a gas station with ill maintained equipment to the effects of 'huffing' gasoline. Sure you can see what above-level exposure to the fumes might do, but it's just not even close to the effects of intentional misuse. Again, not saying it's good, bad or otherwise, just the first comparison that I could think of that translated somewhat well.
I definitely agree with the flavorings, etc. They're meant to be consumed & were never designed to be inhaled. Does that make them bad or dangerous? Not a clue. Diacetyl is perfectly safe to consume. If you drink craft beer, you've probably drank more of it than you can imagine - it's acceptable in some styles & there's a lot of crappy breweries around that can't manage their fermentation to eliminate it when it's not acceptable. That's why "popcorn-lung" was such a surprise. Diacetyl was considered safe for consumption, even in elevated levels, with no thought on the effects of inhaling massive amounts.
ETA: Liquid in the lungs is a completely different story. Very dangerous. That's why the populations of Florida & Louisiana perished many decades ago. People claiming to be posting from the SouthEast are just a part of a government conspiracy. :tinfoilhat: