There is a very interesting map of conscription (compulsory military service) in the world here:
Most of the countries in the developed world do not seem to use conscription. As the site mentions, many countries have done away with conscription.
Conscription is controversial, because of conscientious objection to service, or political objection to service for a disliked government, or an unpopular war, and because it violates individual rights. (enotes reference, conscription)
Basically, in New Zealand you would expect people to be able to have the right to be a conscientious objector. I also do not think New Zealand will be involved in any wide-spread wars any time soon, which is the only purpose for conscription I can see.
Read more here: