How does this protect New Zealanders?

Over the weekend, we learned that the GCSB had been spying on the Solomon Islands, including on a prominent anti-corruption campaigner. The GCSB responded to this by saying that they exist "to protect New Zealand and New Zealanders". Which invites the obvious question: how does this protect New Zealand? How does spying on the government of a friendly nation protect New Zealand? How does spying on their efforts to find truth and reconciliation for their past protect New Zealanders? And most particularly, how does spying on those who campaign to expose corruption in the Solomon Islands government and ensure that it does not steal from its people protect us?

The answer is that it doesn't. None of this spying is justified. And if this is the GCSB's mission, we are better off without it.