Prohibiting ordinary firearms is not a good policy, but if it were a good one, it would have been a good one a year ago — and it would still be a good one a year from now. Acting with a minimum of debate and reflection in the wake of a convulsive national horror may be the easiest way to enact sweeping legal changes, but it also is the worst way.
This is especially true when the question involves the fundamental rights of citizens. That the government of New Zealand does not recognize the right to keep and bear arms as a civil right — a right that distinguishes citizens from subjects — is no more relevant to the question than the censorship enacted by the junta in Beijing is to the status of free speech as a civil right. Governments do not create human rights — they only recognize them or violate them.
Democratic governments violate civil rights most often when their citizens are terrified and angry: That kind of fearful stampeding is how you get nice liberals like Franklin Roosevelt building concentration camps and rounding up citizens for detention based on their ancestry.