I simply don't accept that aircraft cabin air and environment are inherently any more "risky" than any other environment where human beings cluster together
As Nicolas Cage said in
City of Angels ... "Just because you don't believe it, doesn't mean it isn't true"
The fact is, and you can argue this all you want but it it is demonstrable that cabin air is, for the most part, acceptable for the majority of people - including cc - for the time that they typically spend on aircraft. It is also demonstrable that cabin air is
not the same as an equivalent ground-level setting where people are clustered together eg a cinema
1) It is not delivered at the same Barometric Pressure or Relative Humidity
2) It is usually recycled with a smaller proportion of make-up air (some industrial systems for buildings do this also... as in sick building syndrome)
3) There MAY be contaminants - such as oil mist and Tri Cresyl Phosphate inadvertently introduced into the bleed air and which in the latter case is a known neurotoxin. Some aircraft are suspected to be worse than others (anecdotally the 757 and 146/RJ) and some people including pilots & cc - have allegedly been found to be hypersensitive to very low levels of TCP whereas most of us are unaffected.
4) The very basic fact that people tend to travel even if they are sick because typically travel isn't discretionary, but the same people tend not to go to the cinema if they are feeling unwell. When did you last hear of someone getting TB from a coughing neighbor in the cinema? There are loads of instances every year where this happens on aircraft.
So whereas I agree that for the majority of people cabin air is acceptably safe, I don't accept that there is no difference between being in a crowded place for 12 hours or on an airplane for 12 hours. And I say that having spent a good proportion of my life as an Occupational Health Professional when I wasn't analyzing Jet fuel in the lab. When I was 11 years old I was involved in a oil fume incident in a VC-10 (G-ARVI) in Dharan, and I honestly thought I was going to die, I was so sick. A small washer had deteriorated (the FE showed it to me) and allowed oil mist to enter the cabin. Thanks to the promptness of the BOAC cc we were all bundled off (it was a schoolkid special) and made comfortable but since then I have read avidly on the subject. It influenced my career choice.