Human nature
Exactly Moonraker.
Just because you can't see it nor touch it it doesn't mean it doesn't exist. Obviously there will always be conspiracy theorists but I don't think this issues falls into that category.
As I already said, the 2 people I know who fear they've been affected are simply not that sort. Asbestos underwent a similar denial phase with huge amounts of corporate resources thrown at denying any health risk meanwhile people continued to contract fatal diseases. It really is simple. The authorities have a duty to investigate ALL health risks that crews or pax may encounter in a pressurized cabin and it can be done fairly easily.
The more it isn't the more I think they have something to hide. There are too many sane people concerned about it now to simply say it's human nature to find single issues to whinge about.