As the Australian same-sex marriage debate heats up it may be time for cool reflection on the sources of our polarised views. Recent research shines a revealing light on the roots of pro- and anti-marriage equality sentiment. It helps explain the roots of our attitudes to same-sex marriage, and whether they are shallow enough to allow attitudes to change.

Who holds pro- and anti-same-sex marriage attitudes?

A paper published this year by American sociologists Amy Armenia and Bailey Troia reviews research on factors that predict views on same-sex marriage. Several factors are now well established.

Most obvious is political orientation. Conservatives tend to oppose marriage equality. Although they tend to be more religious than liberals, their opposition to same-sex marriage is not reducible to their religiosity.

Religious affiliation and observance are important factors in their own right. People who are religiously affiliated, attend religious services and hold more literal or traditional interpretations of religious texts are more opposed to same-sex marriage. One study found people who viewed God as male were especially likely to be opposed.

A third group of factors associated with same-sex marriage attitudes is demographic. Women, younger people, more educated people and people living in urban regions tend to be more favourably disposed to same-sex marriage.

Are attitudes to same-sex marriage alterable?

It is sometimes argued that attitudes to same-sex marriage are deeply entrenched and attempts to alter them are pointless. Public debate often seems to be conducted by ideological warriors at the righteous extremes, aiming to deride and defeat their adversaries rather than to persuade. Can minds be changed on this issue?

A sceptic might argue same-sex marriage attitudes are hard to change and primarily determined by one’s birth cohort. Young people have more favourable views than their elders, so attitudes will gradually but inexorably shift as one generation replaces another.

On this view, to paraphrase German physicist Max Planck’s famous quote about science, social attitudes advance one funeral at a time.

Armenia and Troia’s review offers some support for this idea. Younger people are consistently more likely to support marriage equality than older people. However, the change in public opinion on same-sex marriage has been too rapid to be explained by generational replacement.

In the US, the General Social Survey shows a rise in support for same-sex marriage from 37% to 55% between 2006 and 2014. Similarly, in the UK support rose from 47% to 60% between 2007 and 2014. This rapid attitudinal change is due substantially to individuals modifying their views.

For example, Armenia and Troia’s analysis shows that 40% of the General Social Survey sample collected in 2008 supported same-sex marriage that year, but in 2012 49% of the same people did so. Indeed, it has been estimated that two thirds of the recent historical change in attitudes is due to people altering their views rather than to generational shifts.

Attitudes to same-sex marriage appear more malleable than we might have expected. In a 2013 survey by US think-tank the Pew Research Center, 28% of US supporters of same-sex marriage reported they had changed their mind on the issue. Most often change occurred as a result of contact with someone personally affected by it.

Although public debate may appear to reflect a battle between adamant, unshakeable positions, our attitudes may be open to influence, persuasion and evolving social norms.

How opponents and proponents of same-sex marriage justify their attitudes

Same-sex marriage attitudes are predictable based on our political and religious beliefs, and our demographic attributes. But what arguments do people with different attitudes appeal to when justifying their position?

A new article by Irish social psychologist Cliodhna O’Connor suggests that these arguments often make claims about what is natural.

O’Connor analysed news media reports in the lead up to the Irish referendum on same-sex marriage in May 2015. She found that the idea of naturalness featured differently in the public statements of same-sex marriage opponents and advocates.

Opponents invoked naturalness primarily in relation to parenthood. They argued parenting depends on “natural ties” and the instincts of biological parents. Alternative ways of reproducing such as surrogacy were framed as unnatural.

Opponents also referred to nature when discussing marriage and gender. Traditional marriage was presented as naturally heterosexual. Complementary male and female gender roles were seen as universal and timeless biological facts.

In contrast, same-sex marriage proponents affirmed the naturalness of homosexuality. Unlike opponents, they presented same-sex attraction as innate and unremarkable. By implication, extending the right to marriage to same-sex couples does not violate the natural order.

The idea of nature is rhetorically powerful, and the two sides in the Irish same-sex marriage debate harnessed it to advance diverging causes. Opponents focused their objections on the supposed unnaturalness of same-sex parenthood, marriage and gender relations. Proponents advocated for a more inclusive sense of what is natural.

Is opposition to same-sex marriage driven by anti-gay attitudes?

O’Connor’s research shows that contemporary opponents of same-sex marriage rarely use overt sexual prejudice to justify their position. This was not always the case.

A 2001 study of attitudes to same-sex parenting found many critics argued homosexuality was sinful. Now, instead of expressing explicitly anti-gay attitudes, many same-sex marriage opponents appeal to their beliefs about factors other than sexuality.

In contrast, proponents of marriage equality sometimes accuse opponents of being motivated by homophobia. They may view opposition to same-sex marriage as intrinsically homophobic. Alternatively, they may see opponents as insincere for failing to declare the real, prejudiced basis for their attitudes.

Who is right? Is opposition to same-sex marriage primarily a matter of religious or political principle as opponents suggest? Or does it largely reflect antipathy to gay and lesbian people, as their critics maintain?

Research by Dutch social psychologist Jojanneke van der Toorn and colleagues suggests there may be some truth to both points of view. They conducted a series of studies in the US and Canada in which they assessed people’s levels of religiosity and conservatism and their degree of support for “gay marriage”. They also assessed anti-gay attitudes, such as endorsement of statements like “homosexual behaviour between two men is just plain wrong”.

The studies yielded very consistent findings. Religiosity and conservatism were both associated with opposition to same-sex marriage and also with anti-gay attitudes. Roughly two thirds of the association between religiosity and opposition to same-sex marriage was explained by those attitudes.

More religious people were more opposed to same-sex marriage primarily because they had more negative attitudes to homosexuality. Similarly, conservatism was primarily associated with opposition to same-sex marriage because conservatives held more anti-gay attitudes.

This research indicates that much of the opposition to same-sex marriage is grounded in sexual prejudice, despite that opposition often being publicly justified on different grounds. But, a modest proportion of conservatives’ opposition was not explained by prejudice. This fraction may reflect principled objections based on conservative political or religious beliefs.

One account of political conservatism proposes that it rests on two pillars: resistance to change and opposition to equality. The first values the preservation of tradition and social order. The second maintains that differences in social outcomes are natural and inevitable.

van der Toorn’s work indicated that opposition to same-sex marriage mainly reflects resistance to change rather than opposition to equality. Proponents of same-sex marriage often criticise opponents for their lack of concern for equality. However, opponents’ attitudes may spring from objections to change rather than from a desire for inequality per se.

International studies such as these do not address the specifics of the Australian context. Even so, they help us understand the beliefs and motives from which our polarised views of same-sex marriage spring. A little understanding might go some way to civilising an increasingly savage debate.