The NatACTs story is that the government can't go into debt directly to build public infrastructure, even if it's projected to last for generations, because it's not fair to make them pay it back. So the solution is to build it with PPPs (Public-Private Partnerships).
The problem with that story, as Simon Wilson and Gordon Campbell point out, is that our children and grandchildren will end up paying at least twice as much for this same piece of infrastructure when built as a PPP.