"nothing to hide, nothing to fear" is not a principle, it is attempt to trip up people into self incriminating themselves.
Flying Lawyer covers that where he says "Have you considered whether aviation safety is better served by investigations in which all those involved are free to speak openly without fear of being prosecuted or by criminal investigations in which anything they say may be used as evidence (against them) in criminal proceedings and in which they have the right not to answer questions?"
You freely admit! "many aircrew seem to think that disclosure is a bad idea is beyond me", then obviously you would be well advised to read/study aviation safety management systems and "Just Culture" information as much as you can. The writings of James Reason would be a good a place as any to start.
The attempted criminalisation of aviation accident and safety investigation by a number of jurisdictions is of genuine concern. These attempts are also an emerging disincentive and impediment to viable investigations and the attendant safety education and benefits to be derived from these investigations.
If accident investigation with criminal and punitive sanctions is such an admirable idea, how come we still manage to kill and maim so many of our fellow citizens on the roads around the world?
Tipsy