I do agree there should be more done to mitigate the risk of failure, but I think it would be a real shame to see them banned outright.
I think a parallel issue is that we don't really have any heritage railways in Ireland (I know there are a couple of small sections, but none of them long enough to really constitute a railway). The Navan to Kingscourt alignment is still almost entirely intact, and it's hard to see it having much use as a future commuter line. If this could be turned into a heritage line, it would be somewhere people could see steam trains running regularly within driving distance of Dublin, and would reduce the need for steam trains to run on the mainlines.
Obviously, it's a question of funding it, and it should come from tourism/heritage funding and not the NTA. This isn't really a RUI issue, I know.