Technofreak:
I agree in principle with the first part of your post but not to the extent of providing a service for the sake of the service where there is no proper demand.
Bluebridge seem to be able to do it without government money and make a profit. Why not NZR?
As I understand it this project was not merely to replace existing ferries but also to provide roll-on, roll-off rail freight service as well. You can certainly argue there is no demand for inter-island roll-on, roll-off rail freight services ... but there is no such service right now, I don't think (definitely could be wrong about that though). As the man once said "If you build it, they will come". We should be encouraging rail freight for lots of reasons including that it gets trucks off the roads so car journeys are quicker and the highways need less maintenance.
And again, you could also argue that they should have done a bunch of studies to better show whether or not that was a good idea - but as multiple examples in this very thread have showed politicians in both camps are not above calling such work wasted tax money and using it for political point scoring either.
And as for Bluebridge - yes, agreed, but that doesn't invalidate the argument at all. Plenty of airlines serve New Zealand and manage to make a profit. So why should we have bailed out Air New Zealand not once, but twice?