I think there are definitely still questions regarding the "safety" of ecigs, especially in regards to flavoring.
Unless you're vaping purely unflavored juice, there is definitely more there than just propylene glycol, vegetable glycerin, and nicotine. Pretending that ecig juice doesn't have any other chemicals or substances in them is just that, PRETENDING.
Now, we know for certain that some flavorings do contain chemicals that are harmful when inhaled. Diacetyl (butter flavoring) is known to cause irreparable lung damage, and has also been linked to alzheimers. Diacetyl substitutes such as pentanedione, acetyl propionyl, and acetoin may be equally if not more harmful when inhaled. Yet there are dozens of different juice flavors on the market that contain these chemicals. To my knowledge there isn't a single study that says the flavorings used in ecig juice are safe to inhale, and the vast majority have never been tested for inhalation safety.
Then there is the possibility of an allergic reaction, either in yourself or in a person who breathes your vapor second hand. Someone with a severe nut allergy may have a serious reaction to your vapor if you're using a natural nut flavor. Someone with an anise allergy could experience the same. You could send someone to the hospital with a life threatening allergic reaction to your vapor with the right flavorings if they have a severe allergy to them.
And rather than asking for studies to prove that ecig flavoring is harmful to be inhaled, why don't you try coming up with some that say they aren't? I probably can't find a scientific study that says if you are isolated in a pure nitrogen environment that you'll die, but if you are, you will. If you want to claim they are safe then the onus is on you to prove it. Otherwise be honest and admit the health risks are unknown and may very well be hazardous to yourself and others. We all assume that it's safer than smoking, but that's really just an assumption, not a proven fact.