So what's next? We all know it won't stop at same-sex unions.
So who's up for group marriage?
For weeks, Sydneysiders and Melburnians who believe menages-a-trois and other polyamorous relationships can be just as committed, loving and valid as marriage between a man and a woman, slaved away together to earn their place in the sun. They drew up plans, sawed wood, hammered nails.
Finally, in early March, it was ready: the first float celebrating polyamory to join the colourful flotilla in the Sydney Gay and Lesbian Mardi Gras.
Here's some background to the movement for "poly pride." They even have their own "community."
The polyamorous community in Australia is a broad church, with the slogan of its very active website being "ethical non-monogamy".
It is increasingly prominent, with organised groups in most capital cities that hold regular discussion sessions and social nights.
Polyamorists generally distinguish themselves from the monogamous gay community, and from those seeking kinky casual sex. Some also see themselves as different from heterosexual polygamists where the "hinge" member has sexual relations with the two of the opposite sex, but the two of the same sex do not have sex with each other.
Rather they may form, in polyamorist lingo, a "polyfidelist triad" in which there is an equilateral triangle of sexual activity.
Group marriage is not without it's trials and tribulations.
A recent Australian legal case involved a man whose wife had left him for another man and a woman, and taken the children. When the trio set up house together, mingled their respective offspring, and shared the same bedroom, the jilted husband applied to the court seeking an urgent order that the children be removed from the "immoral" household.
But magistrate Philip Burchardt rejected the application, saying the threesome seemed to be "thoroughly decent and honest people" and "I do not regard the relationship . . . as being damaging to the children."
What's next after group marriage?
What does this great man advocate?
Singer argues that "mutually satisfying activities" of a sexual nature can occur between humans and animals.
I have a question for those progressive clergy and theologians who have rejected the plain teaching of Jesus. You have rejected the prophets, and apostles. You have rejected 2,000 years of church teaching.
How will you stand against the very forces you have allowed to be unleashed?