I can understand people's reluctance to allow CVR's to be used in criminal prosecutions.
We are all human and human beings make mistakes, and it makes sense to use CVR's to find out how those mistakes happened to put in place systems that will prevent them reoccurring.
However, mistakes are one thing, criminal or gross negligence another. If your husband/wife/kids had been killed on a flight in which culpable negligence was suspected, would you want significant evidence of that negligence to be hidden from a prosecution and, as a result, the (possibly) guilty parties to go free, possibly to commit the same offence again with someone else's nearest and dearest? You have to see the other side as well.
I don't think that unlimited access to CVR recordings or transcripts should be available, though. There's enough already that the press love to make uninformed speculation with.
Perhaps the equivalent of a coroner's court should decide whether there is enough evidence on the basis of their enquiries to decide whether a criminal prosecution should follow, and whether any particular portion of a CVR recording should be used in that prosecution? I am not in favour of either the police or the regulatory authorities being permitted to decide such...