...there are many ex pilots, cabin crew who are absolutely certain and know 100% what caused their normal good health to alter...
...we have various office bound doctors, lawyers, bureaucrats, regulators, politicians 'believing' (hoping) that toxic oil fumes in a confined space are not responsible...
And that's the problem: a lack of proper evidence/research. There should be no need to "believe" in anything: it should come from proper analysis of the situation. It's a bit like living next to a nuclear power station and "knowing" it gave you cancer - this is not science of any sort and unlikely to lead to any changes.
I fly jets with bleed-driven packs, so I am *very* concerned about air quality from a selfish point-of-view. I also have some sympathy for the technical side of the airline industry in that hard data on this subject seems pretty difficult to come by. I've seen a couple of papers but they effectively say: "more research required". Most of the "facts" I hear quoted are such things as "an engineer told me..." or "did you know that...", etc.
There is a temptation to go for a sort of conspiracy theory but considering that the airlines/regulators/investigators have been formally told of this issue on many occasions (and are running studies), it would be rather foolhardy of them to try and cover up something that is so much in the public domain, IMHO. Now that aeroplanes (in the UK at least) are covered under H&S, the sort of fines and lawsuits that would follow discovery of withholding of this kind of information would be spectacular, to say the least.
Also, I hear "just fit filters". What kind of filters are these and what are they filtering? Do they work or are they just like putting a hanky over your mouth during a nerve gas attack (which is the class of chemicals we're discussing). It'd be ironic if the airlines caved in and rushed out some countermeasures which were found to be ineffective some years later.
If I'm giving the impression that I'm unsympathetic to those who are suffering from ill health in their flying careers (possibly from some sort of nervous poisoning), then nothing could be farther from the truth. What I do feel is that we need less emotion and more hard science, otherwise we're just going round in circles.