Al Nisbet's cartoon published in The Press on May 30.

Al Nisbet's cartoon published in the Marlborough Express on May 29.

Prime Minister John Key says it is not possible to change the law to lower the threshold for inciting racism because like pornography racism is subjective.

There have been calls for racism laws to be redefined after Race Relations Commissioner Dame Susan Devoy said Al Nisbet cartoons printed in the Marlborough Express and The Press this week did not meet the legal definition.

The cartoons, referring to the new food-in-schools programme, have been criticised for stereotyping Maori and Polynesian people as spending their money on cigarettes and gambling rather than buying food for their children.

ROSS GIBLIN/Fairfax NZ DRAWING A LINE: Race Relations Commissioner Dame Susan Devoy responds harshly to cartoons by Al Nisbet in the Marlborough Express and The Press newspapers.

Dame Susan questioned whether the threshold for racism was too high.

But Key said it was not possible to change it because like pornography, racism was subjective.

"Pornography is really in the eyes of what the individual thinks," he said.

"There are some extreme examples I think most of us could agree on but then there would be a wide range of views in the community.

"It would be the same thing with racism - something that I might find racist you might not and so I think its one of those things that's highly subjective."

Racism was hard to define in a legal binary fashion so while it was a "nice idea" it was not practical to change the law, he said.

Mana's Ikaroa-Rawhiti by-election candidate Te Hamua Nikora said racism was not subjective when you were the target.

"What the issue of racism requires now is leadership from the top."

The editors of the newspapers have defended printing the cartoons saying they hoped to inspire debate and make people think.