District Court Judge Garry Neilson said just as gay sex was socially unacceptable and criminal in the 1950s and 1960s but is now widely accepted, “a jury might find nothing untoward in the advance of a brother towards his sister once she had sexually matured, had sexual relationships with other men and was now ‘available’, not having [a] sexual partner”.

He also said the “only reason” that incest is still a crime is because of the high risk of genetic abnormalities in children born from consanguineous relationships “but even that falls away to an extent [because] there is such ease of contraception and readily access to abortion”.

Judge Neilson made the extraordinary and bizarre comments in the case of a 58-year-old man, known for legal reasons as MRM, who is charged with repeatedly raping his younger sister in the family’s western Sydney home in 1981.

The man had earlier pleaded guilty to sexually assaulting his sister when she was 10 or 11 years old in 1973 or 1974 after police recorded a telephone conversation between the siblings in July 2011 in which he admitted to having sexual contact with her when she was “a kid”.

But he has pleaded not guilty to the charge of sexual intercourse without consent, with an alternative charge of incest, regarding the 1981 events.

On April 7 a jury was empanelled and the Crown Prosecutor requested the jurors be told of the earlier misconduct to show MRM had a tendency to have a sexual interest in and have sexual intercourse with his sister.

The Crown argued that without the background information, the jury might find it hard to understand why MRM began raping his sister “out of the blue” and why she did not report it to her parents or police.

In the mid-1970s MRM had warned her not to tell their parents because they had just lost another son in a car crash and she remained fearful of upsetting her parents when the abuse recommenced in 1981.

But Judge Neilson refused to admit the evidence, saying the sexual abuse which had occurred when the girl was 10 or 11 and the youth was 17 occurred in a different context to the sex which happened when she was 18 and he was 26. By 1981, she had had sexual relationships with two men and had a young child.

“By that stage they are both mature adults. The complainant has been sexually awoken, shall we say, by having two relationships with men and she had become ‘free’ when the second relationship broke down,” Judge Neilson said.

“The only thing that might change that is the fact that they were a brother and sister but we’ve come a long way from the 1950s … when the position of the English Common Law was that sex outside marriage was not lawful.”

He went on to say incest only remains a crime “to prevent chromosomal abnormalities” but the availability of contraception and abortion now diminishes that reason.

“If this was the 50s and you had a jury of 12 men there, which is what you’d invariably have, they would say it’s unnatural for a man to be interested in another man or a man being interested in a boy. Those things have gone.”

On Tuesday Crown Prosecutor Sally Dowling SC asked the Court of Criminal Appeal to remit the case to a judge other than Judge Neilson because of the "misogynistic" attitude he displayed towards the complainant.

“These remarks in my submission are completely disgraceful,” Ms Dowling said.

"The reference to abortion is particularly repellent.”

Justices Arthur Emmett, Derek Price and Elizabeth Fullerton reserved their decision.

Adults Surviving Child Abuse president Dr Carol Kezelman said: "To equate homosexuality, incest and the crime of child sexual assault is as ill-informed as it is outrageous. For it to be paraded by a Judge in Australia in 2014 during the time of the Royal Commission into Institutional Abuse, or at any time, is beyond belief. Literally thousands of survivors of child sexual abuse have given testimony before the commission of the decades of damage their abuse has caused," Dr Kezelman said.

"The relational betrayal of the horrors of incest between a brother and sister of any age is abhorrently criminal. Failure to understand that prior abuse disempowers the victim establishing the ground for future assaults is ignorant. This together with referring to a sibling as being sexually ‘free’ or ‘available’ demands strict censure."

Bravehearts founder Hetty Johnston called for Judge Neilson to step down from the bench for "ludicrous and obscene remarks".

"These comments are offensive to every child, every victim, every homosexual person in this country."

Ms Johnston also called on the case to be referred to the current Royal Commission into Institutional Responses to Child Sexual Abuse.

SMH