There should be no different way in running a society than the way it's done in New Zealand and in the US:
1. you have a right to defend yourself.
2. you have a right to own firearms, which are the means by which you exercise the right above.
Without the means by which to defend yourself, your right becomes irrelevant. It's effectively denied. Remember the poll tax? A few dollars to exercise your right to vote deprived a lot of people of that right because they didn't have the means...if only the politicians and activists that defended the right to vote considered all the other rights as important as the right to vote...
Now, on to the use of lethal force. I've posted on this before, but here's the essence:
Your use of force must be both necessary and proportional to the threat you face. To use lethal force, then, you must be facing a lethal threat (or near-lethal, the threat of serious bodily harm). A threat consists of three elements: ability, opportunity, and intent. Without all three elements, there isn't a threat, and the use of lethal force in response to the situation becomes a crime in itself.
The ability to harm you, as represented by superior size, strength, numbers, or a weapon. The opportunity to harm you, as represented by proximity. The intent to harm you, as stated verbally by your assailant, or demonstrated by their actions (harming you, presenting a weapon pointed at you, etc.).
And, this is critical, in determining the presence of the above factors, only the knowledge that was available to the person at the time can be used. E.G. if the gun that was presented looked real, and the defender reasonably believed it to be real, then a weapon, a lethal ability, was present, even if it was later shown that the weapon presented was an Airsoft gun...not a real one...
Those are the criteria by which this homeowner will be judged.
It's as true in New Zealand as it is here...interesting that you chose New Zealand as your "alternative" because, frankly, things are closer to the US there than nearly anywhere else in the world. Many nations so restrict the right to firearms that the right of self defense ceases to exist. In those nations, it is presumed that the police will stop crimes...when we all know that the police can't be everywhere, and generally solve the crime after the fact, fulfilling their civic duty in deterrence, but doing little for the direct benefit of the victim.