Federal Opposition Leader Bill Shorten has reasserted his support for same-sex marriage in a speech to a Christian conference, taking aim at those who "insult and demonise people on the basis of who they love".

Mr Shorten made the comments in a speech to the Australian Christian Lobby national conference in Canberra on Saturday.

"When I see people hiding behind the bible to insult and demonise people on the basis of who they love, I cannot stay silent. I do not agree," he said.

"When I hear that people allege that God tells them that marriage equality is the first step to polygamy and bigamy and bestiality, I cannot stay silent. I simply do not agree.

"These prejudices do not reflect the Christian values that I believe in. I think they paint the accusers as people who would rather judge than understand."

During a public question and answer session with Mr Shorten after his speech, the lobby's managing director, Tony Shelton, disputed the claim people have cited God when talking about the link between marriage equality and bestiality.

He said he had "certainly not heard people invoke God with regard to that".

Mr Shorten, who voted in support of gay marriage in 2012 in Parliament, said he would continue to push for marriage equality in Australia, even though for many people of faith it is a vexed issue.

"How can compassion, charity, love, recognition and endorsement continue to be restricted to heterosexual Australia and the nuclear family?" he said.

"Whatever our views about marriage, and whatever our social views about how best to raise and educate children, I do believe that we currently have a law which discriminates against adult couples on the basis of who they love."

Liberal senator Cory Bernardi, who made comments linking bestiality and gay marriage, has tweeted that no-one takes seriously Mr Shorten's lectures on morality and marriage.

Speaking outside the Lakemba mosque as part of National Unity Day, Immigration Minister Scott Morrison said he was a supporter of the existing arrangements around marriage.

"I'm a big supporter of marriage. I think it's great. As you heard from the sheik here today, the Islamic community also strongly, I think, identifies with the institution of marriage.

"I'm a key supporter of the existing arrangements and the Government has no plans in this area," he said.

Freedom of speech does not permit hate speech: Shorten

Mr Shorten also said Australia was a multi-faith country that celebrated diversity.

He said no faith or religion should ever be used as an instrument of division and exclusion, and freedom of speech did not mean the freedom to express prejudice or hate.

"Condemning anyone, discriminating against anyone, vilifying anyone is a violation of the values that we share," he said.

"In our society, under our laws, whether we be Christians, Hindu, Jews, Muslim, Buddhist, or atheist, we are all Australians and we are all equal."

Mr Shorten cited Reverend Martin Luther King as one of his heroes.

"A country should not tell a bootless man to pull himself up by his bootstraps," Mr Shorten said, quoting Dr King.

"He believed about the United States in 1963, that the nation was generous and wealthy enough to ensure that all were included.

"This is the Labor project, the big picture, the higher ground that we strive for."

Mr Shorten also criticised what he described as "deep cuts" in foreign aid.

"I believe Australia is a more generous, more decent country than this," Mr Shorten said.

"I believe we are capable of looking after our people at home and extending a helping hand elsewhere."