I don't mean to suggest that it isn't a legitimate concern when I imply this is a witch hunt - what I mean is, there are some people who are very much looking for something to be concerned about. It's a confirmation bias thing - people have a tendency to find exactly what they look for, if that makes any sense? It's obviously a legitimate concern - and as part of the community myself, I think it bears mention, consideration, and action!
I 100% agree that maintaining lung function should be a primary consideration - I know mine has dramatically increased since I started vaping. If anyone feels like they want to avoid diketones, we'll gladly consult on which liquid contain less of them. At this point I think there are many who believe (either rightly or wrongly) that their "quit" depends on liquids that are presently in excess of what NIOSH or Dr. F consider "tolerable" - and when those consequences are taken into consideration, I doubt one of them would object to any eliquid regardless of the diketone content (if, the alternative was smoking a traditional analog cigarette). I think the point they are making (thankfully, and rightfully so) is that responsible vendors reduce or eliminate constituent ingredients that give reason for pause, or, have the potential for malevolent effect. Even in the absence of evidence, it's a no brainer - minimize and reduce exposure in any and every way possible (if it matters to the end user). Surprisingly enough, many (even most?) vapers could care less - as long as it's not a cigarette, it's fair game. I'm not here to judge... I'm just here to provide top quality eLiquid consistently in a clean environment - and - do so with a level of transparency and integrity. I also view my role as somewhat of an educator since even if I reduce all the levels of the above to Non-detecteable levels - most vapers will still be vaping it whether they get it from me or not. Most vendors (90% or more) don't have the faintest idea what's actually in their own bottles. It's an education thing for me, also - I am constantly learning. I read quite a bit on the subject - I just haven't seen any compelling evidence that we should make any drastic changes.