Sydney District Court Judge Garry Neilson said that incest is becoming socially acceptable as in the case of homosexuality which was previously perceived as a crime back in the 50's and 60's.

Neilson made the disturbing statement as he sits for the case of a 58-year-old man who was being tried on charge of repeatedly raping his younger sister back in 1973 or 1974.

The man pleaded guilty to the charge of rape when his sister was just 10 or 11 years old. However, he pleaded not guilty to the charge of sexual intercourse without consent when he had sex with his sister when the latter was already 17, 18 and 26.

"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. 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," Nielson said.

He boldly said that incest only remains a crime "to prevent chromosomal abnormalities" but that too will be abolished soon as there are already contraception available and abortion becomes a choice.

"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... 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," Nielson said.

Adults Surviving Child Abuse president Dr Carol Kezelman and Bravehearts founder Hetty Johnston condemn Nielson for his disturbing remarks.

"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. This together with referring to a sibling as being sexually 'free' or 'available' demands strict censure."

" Kezelman said.

"These comments are offensive to every child, every victim, every homosexual person in this country," Johnston said adding that Nielson should step down from the bench.