That doesn't necessarily make his decision wrong. He will argue that Isis poses a grave threat to the stability of an inter-connected world and we must do our bit. The fact that NZ now has a seat on the United Nations Security Council adds weight to the argument that we must be seen to be a "good citizen".
And it is probably true that in a globalised world with its advanced communication technologies and ease of travel, we could not have stayed immune forever from the brutal acts of those at odds with the Western democratic perspective.
But it is to be hoped that our "opposition to terror" does not over-run our civil liberties and, while Key has admired Australia and its premier Tony Abbott's sabre-rattling, he should be cautious about following our neighbour's example.
Australia has just enacted laws - on behalf of the "war on terror", of course - that make it illegal to report matters of national security, while a report or advert that could be considered as aiding recruitment for a foreign army now carries 10 years' jail time.
A free press, a foundation of a democratic society, could now be a casualty in this "war".