If a single young person takes their own life because of the anti-same-sex marriage campaign during a planned plebiscite, that will be one too many.
Labor leader Bill Shorten delivered that blunt warning to parliament on Monday as he introduced legislation to make the change without the need for a national vote.
"A no campaign would be emotional torment for gay teenagers," he said on Monday.
"The idea of young people, perhaps yet to come out, seeing the legitimacy of their identity debated on the national stage - that is not an ordeal we should inflict on any citizen when we have a better path."
Achieving marriage equality should be a joyous, unifying occasion, he said, calling on Prime Minister Malcolm Turnbull to dump the government's planned plebiscite.
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His comments came as the gay community, their families and supporters called on politicians to back a parliamentary vote.
"We fear for our children and we fear for older and younger LGBTIQ people," Parents and Friends of Lesbians and Gays spokeswoman Sharyn Faulkner told reporters in Canberra.
"The mental health issues will be astronomical, the money is wasteful and we just need to get on with this."
Her group arranged for almost 200 gay and lesbian leaders to sign an open letter asking politicians to block the plebiscite.
Signatories include comedian Magda Szubanski, Olympic gold medalist Matthew Mitcham, writer Benjamin Law, and radio host Julie McCrossin.
On Monday afternoon, parliament will receive a petition signed by 57,000 Australians who want a free vote on marriage equality in parliament instead of a plebiscite.
Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14 or the Suicide Call Back Service on 1300 659 467.
