The so-called "homosexual panic defence" has historically resulted in more lenient sentences for such defendants.
Now Barnett is considering introducing a private member's bill to eliminate the defence after growing concerns about men being convicted of manslaughter, not murder, when they kill gay men after a sexual approach.
He has asked colleagues to draft a bill and hopes to introduce it within the next two or three months.
The Law Commission is also examining the issue and is likely to recommend repealing section 169 of the Crimes Act, which allows for a defence of provocation. Commission deputy president Warren Young said it was likely to recommend the repeal because matters suich as provocation should be considered in sentencing.
It is 20 years today since the controversial Homosexual Law Reform Bill became law. But many are still critical of a legal anachronism which allows a defendant to get away with manslaughter, not murder, if he argues he was panicked into attacking someone who provoked him by an unwanted sexual approach.
Three years ago Auckland celebrity interior designer David McNee was bashed to death by transient Phillip Layton Edwards. The defence successfully argued that Edwards, who had 56 previous convictions and had been on parole for 11 days, was provoked into beating McNee after the former television host violated their "no touching" agreement. Edwards was jailed for nine years for manslaughter.
The law change issue is canvassed in a Victoria University Law Review paper by associate law professor Elisabeth McDonald, due out in six weeks. McDonald argues that the provocation defence invariably arises out of a defendant's homophobia and should not be treated as a mitigating factor.
It was mainly used by "men who get angry and kill someone", she said.
A group of human rights activists says the homosexual panic defence would never be justified in a murder involving a heterosexual victim. Among them is Aids Foundation chairman Jeremy Lambert, who said the defence, which is part of common law rather than statute law, was an "absurdity".
"This is a particularly hideous piece of law that was made on the sly. It can mean you would never be found guilty of murdering a gay man."
The McNee case was a classic example of the law not protecting gay men, Lambert said.
"It's abhorrent to suggest that we should downplay the seriousness of what Edwards did because he was hit on."
Young said the current law relating to provocation was muddled and very difficult for lawyers and judges to understand, let alone a jury. It had originally existed as a partial defence when New Zealand still had capital punishment and a mandatory life sentence for murder. But changes to sentencing laws had given judges more discretion over mitigating factors such as provocation.