Under the 2002 Terrorism Suppression Act, fighting alongside or supporting groups like Isis is already an offence imprisonable for up to 14 years. The state also has the power to cancel the passports of those considered to be a threat to national security.
But for the Government, that's not enough. It wants to make it easier to both prosecute those taking part in foreign wars, and to cancel passports for longer.
Mr Key fears that mercenary New Zealanders returning home won't know when to stop their killing ways. If that's so, then why is he mucking around? Let him do a proper job and outlaw New Zealand passport holders from joining any foreign army or crusade fullstop.
After Monday's Cabinet meeting he said there are 3000 Isis fighters with Western passports, including a small number of Kiwis. He warned, "They threaten to return to their countries of origin both radicalised and with military training." Is he not aware that a similar number of foreign recruits are also serving in the Israeli military, including from Australia and New Zealand?
If it's a risk to national security for New Zealanders to fight for one of the warring parties in the Middle East bloodbath, then why is it acceptable for them to be part of another, in particular the Israeli Army which now faces allegations of committing war crimes during its recent 23-day offensive on the Gaza Strip. Should death by beheading be seen as despicable, while firing rockets from a gunboat into a group of kids playing soccer on a Gaza beach, or targeting homes full of civilians, not?
In August, the Age in Melbourne featured New Zealander Sam Gosling who moved to Melbourne in 2008 then joined the Israeli army in 2013. Recovering from shrapnel wounds received in the Gaza bombardment, he was one of 10 members of a Melbourne youth Zionist movement who had joined the Israeli army in the past two years. "What drives them is a love and passion for Zionism," said Zionist spokeswoman, Romy Spicer.
In other words, he is both radicalised and trained for war. Outside the Middle East, what about true mercenaries like former Auckland Sacred Heart College student Eamon Tolhurst who in 2010, joined the French Foreign Legion.
After months of intensive weapons and combat training in the south of France, he has fought gold smugglers on the French Guyana border with Brazil then in 2012 was reported heading for service in Gabon, West Africa.
He doesn't even have a cause, just a French passport, false name and training to kill.
Then there are those who leave New Zealand to join the British, US, Australian - and who knows which other - armed forces. In 2010, the Daily Telegraph in London noted that five New Zealanders had died in Afghanistan serving in four different armies. To be consistent, Mr Key should be criminalising those serving in all foreign armies.
True, the Isis movement seems particularly medieval, even by the standards of that part of the world.
But using it as a bogeyman to push through laws giving the State new powers to restrict civil liberties, far from protecting us, takes us a step down the Isis path.
