“The more grog I got into him the more feminine he became,’’ Entsch recalls.

“I used to tell him to stop acting like a sheila.’’

Years later, Entsch spotted his drinking mate in an outback beer garden, wearing “shorts and a boob tube’’, after a sex-change operation.

His transgender friend eventually moved to Melbourne and trained to be a doctor.

“My mate became a woman,’’ Entsch tells The Saturday Telegraph.

“I often reflected how hard it must have been for her living in that environment, and the courage it took for her to do what she did.’’

The experience changed Entsch’s views about homosexual and transgender Australians.

Forty years later, the Liberal Party MP from cowboy country in far north Queensland is sponsoring a private member’s bill to legalise same-sex marriage in Australia.

If Australians vote Yes for marriage equality in the postal survey that began this week, the bill will be debated in Parliament.

The survey is more than a measure of Australia’s social mores. It is a political and legal minefield, pitting “rainbow activists’’ against religious groups and rupturing the conservative side of politics.

The Australian Bureau of Statistics survey is a voluntary and non-binding alternative to the Turnbull government’s promised referendum, which was blocked in the Senate last year.

The $122 million opinion poll has whipped up a furious debate over discrimination, free speech and religious freedom.

It has provoked public discussion of sex, religion and politics — the very three topics considered taboo for polite conversation.

Gay rights activist Benjamin Law set the tone this week by tweeting: “Sometimes find myself wondering if I’d hate-f. k all the anti-gay MPs in Parliament if it meant they got the homophobia out of their system.’’

Kevin Rudd, the former Labor prime minister, then tweeted a photo of his godson Sean Foster, bleeding from a gash on his forehead.

The 19-year-old musician told police he was bashed for confronting a man taking down rainbow flags in Brisbane.

The vitriol and violence forced federal Parliament to pass temporary emergency legislation this week. Anyone who vilifies, intimidates or threatens to harm other people based on their religion conviction, sexual orientation or gender identity during the seven-week survey period will risk a $12,600 fine.

Conservative Liberal senator Eric Abetz, who opposes same-sex marriage, says “bullying’’ from the Yes camp is a harbinger of how the LGBTI lobby will campaign against religious groups once same-sex marriage is legalised.

“The vitriol has very much been one-way traffic — we’re not the ones calling people names like ‘homophobe’ and ‘bigot’,’’ he says. “People should be free to say if they’re voting Yes or No.’’

“I understand there are people who will be minded to vote Yes, but who are rightly concerned about freedom of speech and freedom of religion and parental rights.

“If a child has the benefit of both parents, and have a male and female role model, that will be better,’’ he adds.

“But if the law is changed, would we still be allowed to say we believe marriage should be between a man and a woman?

“People are telling me that would be seen as vilification and falling foul of anti-discrimination laws.’’

The No camp fears precedents set overseas. In 2012, a gay couple took legal action against a Christian baker in Colorado who said he would not make cakes for same-sex weddings, based on his beliefs. Five years later, the case is headed for a US Supreme Court hearing. The Trump administration is backing the baker.

After Ireland legalised same-sex marriage in 2015, an evangelical Christian baker in Belfast was fined for discrimination on the grounds of sexual orientation, after he refused to decorate a cake with the slogan “Support Gay Marriage’’.

In Washington, a florist is being prosecuted and sued for discrimination after refusing to prepare flowers for the wedding of a gay customer, on the grounds of her Christian beliefs.

Entsch’s bill sets out protections for religious freedom, by stating that ministers of religion can refuse to solemnise a same-sex marriage if the religion only allows heterosexual couples to marry.

Civil celebrants who register as “religious marriage celebrants’’ may also refuse to marry gay couples.

The loophole extends to businesses owned by religious groups, such as schools, halls or catering facilities.

In line with existing anti-discrimination law, any refusal must conform to the “doctrines, tenets or beliefs’’ of the religion and be necessary to “avoid injury to the susceptibilities of adherents to that religion’’.

It stops short of shielding other businesses from an anti-discrimination claim if they refuse to serve same-sex couples on the grounds of a “conscientious objection’’.

Entsch — a married father-of-four who has worked as a crocodile farmer, mining fitter and turner and real estate salesman — insists that businesses should not be allowed to discriminate on any grounds.

“You can’t say, ‘I won’t bake a cake for a blackfella or a Jew’,’’ he says.

“If they did that today, they’d be done for discrimination. Anyway, the next big surge will be gay weddings — wedding planners and cake makers will be fighting to get that market.’’

The Yes side appears to be winning popular support. Tens of thousands of gay marriage supporters rallied in Sydney on Sunday. Cricket Australia, the Football Federation, the ARU and the NRL have all taken a public stand for marriage equality.

Hundreds of businesses have thrown their support behind the Yes campaign, including Kmart, Lendlease, Apple, Westpac, the Commonwealth Bank, Optus and Telstra.

Qantas chief executive Alan Joyce put his money where his mouth is, donating $1 million of his own cash to the Yes campaign.

Church groups are bearing the flag for the No campaign by backing the Coalition for Marriage, which insists that “changing the law on marriage affects everyone’’.

It claims a Yes vote would “give license to activists who will weaponise anti-discrimination laws’’ to target people who believe marriage should be the union of a man and a woman and the foundation for families.

The Australian Christian Lobby (ACL) is hosting “campaign training sessions’’ for supporters to “get the training you need to confidently speak to friends, family and neighbours.’’

It views same-sex marriage as a threat to “traditional marriage’’ and to nuclear families.

But Liberal Party president and former NSW premier Nick Greiner regards marriage as “the conservative ideal’’, arguing that extending the institution of marriage to same-sex couples will “deliver stronger families and communities’’.

In this battle of the sexes, marriage is the final frontier. In the past nine years, 84 Commonwealth laws have been amended to stop discrimination against couples on the grounds of their sexuality — across family law, social security entitlements, immigration and tax laws.

But state laws differ, so legal recognition of same-sex marriage would give gay couples the same legal rights as every other married couple, regardless of where they live.

Under the Family Law Act, same-sex couples and heterosexual de facto couples have the same property rights as married couples if they have been living together for two years, or have a child together.

Same-sex couples have the right to adopt children in every state and the ACT — only the Northern Territory prohibits same-sex adoption.

In March, the NSW Supreme Court let a lesbian couple adopt a four-year-old girl despite opposition from her Catholic birth parents.

The baby had been taken from her mother four days after birth. The mother had a long history of drug addiction and had been convicted over the death of her baby son seven months earlier, from drug poisoning.

The judge let the lesbian couple, who had been caring for the girl since she was a baby, to adopt after they agreed to send her to scripture classes and read stories from the Bible.

If the Yes vote succeeds, any changes to the Marriage Act will require a majority vote in federal Parliament.

The law has been changed 20 times; most recently in 2004 when former prime minister John Howard inserted the words “man and woman’’, to prevent gay couples having their overseas marriages recognised in Australia.

Prime Minister Malcolm Turnbull has announced the government will not introduce its own legislation, but will ask MPs to vote on a private member’s bill — most probably the one by Entsch and four fellow Liberals.

Howard savaged Turnbull on Thursday, accusing him of jeopardising Australians’ right to freedom of religion and speech. He said Turnbull should first spell out the “protections’’ for people who boycott same-sex marriages on conscientious grounds.

“If a Yes vote is recorded there will be overwhelming pressure to move on, legislate as quickly as possible, and then put the issue behind Parliament,’’ he said.

Legislating for marriage equality will not be as simple as removing the words “man and woman’’ from the Marriage Act.

The federal Attorney-General’s Department estimates that 25 pieces of Commonwealth legislation will require up to 60 individual amendments.

The postal vote closes on November 7. A week later the results will be made public, and it will be clear whether conservatism has rained on the same-sex wedding party.