I wonder whether the differences of opinion in this discussion are to some extent influenced by the fact that (professional) helicopter flying in the UK is predominantly military, off-shore transport, emergency services and executive transport with very little 'utility' flying of the sort very common in some other parts of the world.
We know, from several threads on this topic over the years, that leaving helicopters unattended with rotors turning is a widespread practice in some parts of the world.
We also know that there are sometimes accidents as a result.
Is there evidence of a high number of accidents relative to the frequency of the practice?