Marriage is not about romance and legalising same-sex marriage is a threat to terms like 'mum and dad' and 'ladies and gentlemen', according to Liberal MP Ian Goodenough.
Mr Goodenough believes same-sex marriage would raise social and legal complexities, cause mental health problems and weigh heavily on the health system.
"Marriage is not a romantic notion, it is a important social institution that deals with progeny," he told parliament on Thursday while arguing for a national vote on the issue.
The romance-less definition prompted Labor colleague Terri Butler - a strong advocate for a change to the Marriage Act - to issue the MP some dating advice across the chamber.
"If I was to counsel the member for Moore in his quest for love, maybe don't roll that one out on the first date," she told the MP.
"I do think we may have found an explanation for his bachelor status."
Mr Goodenough, 41, fears legalising same-sex marriage would render terms like mum and dad and ladies and gentlemen politically incorrect.
"Our language may have to change."
Mental health issues would sprout from more complex relationships.
Children would be born into three-way relationships as it is biologically impossible for same-sex couples to have babies.
And Mr Goodenough believes no case has been made as to why civil unions aren't good enough.
Fellow WA Liberal MP Andrew Hastie also argued against a law change, saying the debate was about the character of marriage not about people's sexuality.
Marriage was a comprehensive union between a man and a woman, he said.
"Comprehensive because it involves both mutual consent and sexual union that is inextricably linked to procreation and the continuation of the human race."
The Turnbull government's planned plebiscite appears doomed after Labor formally rejected the idea and most of the crossbench in the Senate oppose the establishing legislation.
Labor wants a free vote in parliament.
Nationals leader Barnaby Joyce insists there is no alternative to a plebiscite, counselling MPs against a split within the coalition over the issue.
Nationals MP George Christensen says the governing coalition would be under threat if Prime Minister Malcolm Turnbull came up with an alternative.
"When you're breaking one of the fundamentals of the coalition deal you've obviously decided to break the coalition deal," the MP told Sky News.
"There would be some serious repercussions."
Mr Joyce said he had not spoken with Mr Christensen but had some advice for all party members.
"I always think at the back of the (rugby) lineout or when you are working in a pub as a bouncer - don't make threats, have people understand clearly who you are," he said.
The deputy prime minister, who supports the existing marriage definition, said it was clear there was no "Plan B" when it came to the coalition's position on same-sex marriage.
"This (the plebiscite) is a decision that was taken to the Australian people," he said.
"Our Plan B is balance the books, build the dams, get inland rail going ... keep our agricultural exports going - that is the plan."
