Re #20 “Filter bleed air - it is NOT rocket science”.
There are many problems: what are you filtering out, what is the contaminant / particle size? - see above.
What happens when the filter is full / blocked, if it subsequently fails do you expose people to a higher risk?
A quick look into many air-conditioning systems reveals a chemistry set consisting of old engine or hydraulic oil, de icing fluid, re circulated dirt/dust/detritus. What are the chemical processes that could occur with change of temperature / pressure / humidity during flight? How many of the serious events have occurred during descent – could there be a clue there?
A natural human reaction is to experience concern when encountering an unknown – the sense of smell can contribute a flee / fight reaction which in high stress situations / personal susceptibility (either personality or situation induced, e.g. fatigue) can contribute to actual or perceived physical deterioration. This is not to dismiss several well documented and as yet unexplained instances of crew incapacitation, but without knowing what the threat is, the range of defences might be restricted to reactive resources – use oxygen masks if smoke / fumes are encountered. Aspects of airmanship require us to control the stress of surprise – assessing the situation, protecting ourselves so that as crew we can fly the aircraft safely – rule 1.