Night flying (outside of flying over built up areas with lights) has to be considered to be instrument flying.
There is no way to orient the helicopter's attitude, height or position with respect to references on the ground.
The problem then becomes comparing instrument flying as we've come to know it with helicopter instrument flying. In most instrument flying, the purpose is to maneuver yourself to a position where you can transition to visual references to land, and the landing is going to be to a well defined piece of turf, typically a lit runway.
Once we realize that, we'll think more carefully about helicopter flying at night, especially to places like oil rigs in the middle of nowhere with a confusion of lights, most of which have little to do with the helicopter.
As for the other places where there have been problems with flying at night - just consider a fixed wing airplane in the same situation and consider the differences.
Sorry for the general nature of the discussion, but it would take too much room to discuss each accident (and I don't have all the details either).