New Zealand's participation in WW2 was clearly about self-protection, not just about protecting others. It was part of the collective security of the British Empire, on which our trade routes and economic life then depended. And it was understood as such. New Zealanders would not have been prepared to make such sacrifices otherwise.
I make a distinction between self protection and self interest. Yes, New Zealand certainly had a real self interest in being involved in the Second World War, but it was under direct threat of invasion, and was not directly attacked in the way, northern Australian towns such as Darwin and Broomer were attacked. And I do think that difference is partly behind the difference in modern attitudes within Australia and New Zealand.
I don't intend to disparage New Zealand in any sense. I've served alongside New Zealand Defence Force personnel on several occasions, and in terms of ability and dedication they are the equal of any on Earth. And, frankly, I feel New Zealand's contribution to World War II is all the greater because of the fact that they were fighting to defend others more than they were themselves. Yes, there was self interest involved and that was important. But self interest has real limits.