Parliament's repeal of the use of provocation as a partial defence for murder does not have widespread support from the legal community.
ACT was the only party to oppose the repeal bill which passed last night by 116 votes to five.
Wellington lawyer Robert Lithgow, QC, said the repeal was "purely political grandstanding" which served no useful criminal justice purpose.
"It means that people who are in bad domestic, bad sexual circumstances, if they react with a loss of control they are treated the same as a cold-blooded killer."
Mr Lithgow said he knew of cases where women and young people who had been abused or subjected to sexual abuse had benefited from the provocation defence.
"Now they're convicted of murder and there's no real last mechanism by which High Court judges could give them sentences that would have previously given."
Auckland lawyer Chris Comeskey said the repeal was a "knee-jerk reaction" after the defence was used in some much publicised and unpalatable cases.
However, in those instances the defence had failed which, if anything, proved juries were capable of making informed decisions.
"The problem (now) is it takes away from the community saying what (the crime) is.
"Traditionally the public could determine what level of anger was acceptable in terms of reducing the charge.
"Because there are situations where a person, understandably so, can get so provoked."
"If you caught an abuser abusing your child, the law now expects you to show the restraint of a saint. Because if you lashed out and death ensued, now you are in very serious trouble."
Mr Comeskey said the provocation defence was originally introduced because there had been a need for it.
Dunedin murderer Clayton Weatherston ran the provocation defence when on trial for stabbing his former girlfriend Sophie Elliott 216 times.
In July, Ferdinand Ambach was found guilty of manslaughter rather murder after killing 69-year-old Auckland gay man Ronald Brown.
Mr Brown was beaten with a banjo before the instrument's neck was rammed down his throat. It was alleged Mr Brown made sexual advances to Ambach.
Weatherston and Ambach have both mounted appeals.