This is exactly the problem you present: Anyone who suggests that evidence is needed is accused of having "personal suspicions" and then presented with some hysterical comment about gas chambers. Such comments help no-one.
I have no horse in this race, no benefit on either side, no profit to make. I'm a scientist by profession and that means that I know what proper evidence is. I've not seen any of that presented thus far, only suspicions and suppositions.
If the problem is as significant as you suggest then it should be relatively easy to gather evidence to support this (financial investment aside). You need medical reports and air quality samples from a large number of flights. You do not need vague reports and "is believed" style statements.
Let's assume that 'toxic air' is definitely a thing. How will you force airlines to take it seriously? Forum posts and hysteria? Or cold, hard, facts?