Brisbane Archbishop Mark Coleridge said those participating in the same-sex marriage postal survey should consider that the love of same-sex couples is different to the love in a traditional marriage, ABC News reports.
"That love is like the love of friends," Archbishop Coleridge said. "It is love and it is valuable, but it's not and it can't be the kind of love that we call marriage."
Archbishop Coleridge said there had always been discrimination towards some forms of marriage.
"Parents can't marry their children, children can't marry their parents," Archbishop Coleridge said.
"Sibling marrying sibling has always been ruled out. People underage have been disqualified from marrying, but so too people of the same sex."
Queensland director of the Equality Campaign Peter Black said he believed the majority of Australians and Catholics saw the love between a same-sex couple as the same as the love shared by a man and a woman.
"All we are asking for is for same-sex couples to be treated with the same dignity and respect as all other relationships," Mr Black said.
"The law should recognise and reward that commitment that those couples are making. I think it's quite concerning to link the idea of siblings marrying siblings or children marrying adults to the idea of same-sex couples."
Archbishop Coleridge said he was not speaking simply from a religious point of view and said language had become "slippery" in the same-sex marriage debate.
"I am concerned to clarify the language and I don't think it's enough to say that 'love is love'," he said.
"There's only one form of love, [of] the many forms of love, that we call marriage and that is between a man and a woman, supposedly lifelong and supposedly open to children."
Archbishop Coleridge said while it was his responsibility to equip fellow Catholics with knowledge about the debate, he did not want to give a "hard time" to people in same-sex unions.
"Their dignity has to be respected at every turn," he said.
Mr Black said the Archbishop was entitled to express his view.
"He has done so in a way that is respectful which is want we want this whole process to be," Mr Black said.
Parent-child marriage cited in urging a No vote on SSM (The Australian)
No campaign sends SMS ad despite their own condemnations (The Chronicle)