New Zealand would be thrilled to have a security guarantee! As it stands they love to criticize Western governments relentlessly while having practically no defense capability whatsoever.
There's already ANZUS, as I'm sure you know. But all being part of NATO would be a much better guarantee.
The United States suspended its treaty obligations towards New Zealand in 1986.
who would attack NZ? Tonga? Samoa? It's a long way from Peru. Plus, aren't the Maori pound for pound some of the best fighters in the world? And for what, a good place to shot Lord of the Rings movies?
edit-as for the OP, yes, of course. The world would be a safer place if we did. We shouldn't be scared to include countries with "issues" either, internal or external. "issues" need solving and what better way than overwhelming military force directed by a coalition of liberal democracies? Of course that's how many "in the not to distant future..." type sci-fi films start, but never mind that. This is the real world, what could go wrong?