Even if he were right, most of us would like to think that New Zealand, being a country, has higher standards of integrity than McDonald's, which is a corporation.
When Key tried to shift the argument and point the finger at cavemen - whose fires, he claimed, also had an environmental impact - he left many bewildered.
But let's do him the favour of considering this point seriously. No one knows exactly how many cavemen there were, although best estimates are fewer than one million before we invented agriculture and moved to town. Accordingly, we can't be sure how much pollution their fires caused, but best estimates are that it was less than the amount generated by 4.5 million New Zealanders and our six million flatulent cows.
"The vast bulk of New Zealand waterways are safe to swim in," said Key.
For someone who made his fortune in the mathematically complex world of currency trading, the PM shows a poor grasp of how numbers work. In numerical terms "vast bulk" and "100 per cent" can be quite some distance apart.
Key seems to regard the argument as nothing more than a hair-splitting piece of sophistry. It's not. New Zealanders are proud of our image and of our tourism industry, so we would like them to be aligned in the way they represent us. Rather than hear him saying our slogan is meaningless, we'd like to hear him saying it's true our rivers and lakes are polluted and this is what we are doing about it.
As a nation we crave attention from the great world; the merest glance is as opium to an addict for us. This week, however, you may have been disappointed by a slightly wry tone to some of that attention. Sainted lexicographer Robert Burchfield, regularly named in lists of greatest ever New Zealanders, has been outed as an idiosyncratic censor who secretly deleted words from the Oxford English Dictionary when he was revising it. This revelation provoked satirical comment about crimes against Scrabble.
Hobbit publicity has also drawn its share of satirical comment. Very well. We must roll with the punches. But I draw the line at being described as "like Britain in the 50s", by a Daily Telegraph journalist, when his country's capital still stops traffic once a day so some soldiers on horses can swap shifts in front of a palace.