My opinion is that vaping is safe, but it's not fool proof. I don't mean to scare anyone, but I've vaped a disposable e-cig from China that gave me a throat infection, so I make sure to shop for American-made juices that aren't produced in big chemical factories, and I haven't had any issues since. The infection was brought on only minutes after I vaped it, never having a throat infection in my life, and the doctors couldn't find a viral source, they were pretty bamboozled by it but just gave me medication and I suffered for a week. It was terrible.
However, it goes a little bit beyond the juice. I personally have a big theory that a lot of coil builds (which is what heats the juice) can cause some throat irritation based on how well they wick, because there can be feed-off particles from wicking material (proven), though these particles, by esteemed experts, are said not to lodge themselves in the lungs in any way. However, with experience, I think that they can indeed cause temporary discomfort. There's also the chance that oils and machine residue can be in tank or wick systems, so cleaning with alcohol or distilled water can be an important step.
By all accounts, if something tastes funky, if you're tasting a sort of singed tasted or metallic taste, it's safest not to vape it. A healthy vape should taste full in flavor, and should be soothing instead or harsh or dirty. Vaping, at its best, should also help people with coughs or lung problems, instead of agitating them. To me, it's always wisest to vape with 0mg juice on any new tank or device, to test and check for any throat irritation or negative tastes - nicotine can really pepper up a juice and also give some discomfort, so it can be confusing as to what to look for.
Other than those issues, the scientific opinion is that vaping is entirely healthy - even moreso than simple "risk reduction." Now, with issues such as wicking particles in a vape, or long term side-effects of vaporizing flavorings or other chemicals (sugars, propylene glycol - which is a healthy chemical to breath in as it is, it's used in hospital air conditioning systems to help combat airborn illness, if I'm not mistaken), it's hard to prove those things either way, but people have been vaping for years now, and with how various professionals do vape, like doctors, or our reviewer Phil, who does voice work and stuff, no one seems to be reporting any issues, or even minor ones, like vocal changes or worsening of breathing.
For me, experiencing a nice, clean vape instantly helps my breathing and relaxes my cough, and also breaks up lung fluid. For me, it's a miracle cure. However, I have to really watch out on wicky-tasting devices, as they do irritate my throat. Healthy flavor, to me, goes hand-in-hand with a healthy vape. Humans have a unique ability to taste if something doesn't taste healthy to our bodies (even if people love sugar, sugar isn't exactly unhealthy - I'm talking more like chemicals and poisons) and my stance is that I just won't vape anything that to me, doesn't taste or feel right.
My motto is that you can't really just think "Ok, this e-cig tastes pretty odd or bad, but cigarettes do too, so this must be safer." I don't believe that's true. Sure, off-brand tobacco flavors are pretty rank in terms of taste, but it's a big difference from like an artificial tobacco taste, and a taste that seems more sourced from singed material or a metaliic tinge, or a burnt vape. If something doesn't taste right to you, I think it's best just to put it down and find something that vapes a lot better.