Flavorings can contain some scary sounding chemicals and some of those chemicals in full concentrations are quite dangerous.
And nicotine in full concentration is very deadly.
If you want to have real fun, look up the MSDS's for phosphoric acid like is found in Coke and Pepsi and most other soft drinks. Seriously, look it up. It is incredibly dangerous too.
Now, consider the concentrations. Concentration is much more important than anything else. Drink too much water and you will die. Drink too little you will die. Too much potassium in your blood will kill you just as too little will.
So, yeah, there are dangerous chemicals in lots of stuff even in perfectly good fruit and vegetables, but in the concentrations they occur, they are harmless. A lot of "junk science" relies on the the notion that if full concentrations of a substance is bad, then any amount is just as dangerous.
Then compare the chemicals that are naturally present in tobacco and the chemicals they put on it during processing to what is in e-
juice. A rational person would choose the juice, but not all people are rational. Debating with irrational people is like trying to teach a pig to sing. That pig will never sing and you will just get frustrated.
And when studies on e-juice do start coming out, look at the process. Will it be like the tests done by the government on a certain herb where they put gas masks on apes and pumped straight smoke into them for an extended time and concluded that since there were signs of brain damage after that test, then smoking any of that certain herb will cause brain damage? Or will the study be done more logically? Who knows?
Meanwhile do what seems right to you. Let the rest lie and don't try to teach that pig to sing.