I often think of the analogy of surgeons. Would, in todays climate, any surgeon accept the situaton where any operation they performed was to be video taped, and that tape was then available for annalysis and possible crimminal or civil action if any Plantif lawer could draw the insinuation of negligence.
The waiting lists for operations would suddenlt get VERY long!!
Similarly, the only way that pilots worldwide accepted the introduction of CVR/FDR and more latterly QAR type devices in the first instence was on the basis that they be used soley for the enhancement of flight saftey, not for disciplinery or criminal/litigious evidence.
One exception to the above that might be of interest to you is New zealand, where CVR data was used to pursue a criminal case against thepilots of an Ansett NZ Dash Eight following a crash in which a cabin crew member was killed. The world-wide reaction to this, and the extent to which the investigation of the accident was hampered by rules of evidence, presumtions of innocence etc. quite clearly demonstrated why use of this data by law enforcement is contrary to the devices primary purpose of saftey enhancement.