Morally ok? That is subject to opinion. I don't have a problem with them now, and I never did.
Legally immune? They very well could be. Certainly any action against them is going to be much harder this time, if only because a bunch of people in New Zealand are still pissed about what happened last time without the revisions that were made. If their system works as they claim, and renders them unable to govern content, then how could they be considered culpable for content? If I start posting nasty stuff encrypted with PGP to HN, would HN be to blame for failing to recognize the nasty stuff and remove it?