Why gay marriage divides the world

The split over same-sex unions is more than ideological. It has deep moral and psychological roots

SO NOW we know: US president Barack Obama is in favour of same-sex marriage. After evading the question for months, he finally made his position clear in a TV interview. "For me personally, it is important for me to go ahead and affirm that I think same-sex couples should be able to get married," he told ABC. The battle lines are thus drawn over what is sure to be an explosive issue in the US election.

Proponents of gay marriage in the US could take a few pointers from the British prime minister, David Cameron. Last September, he famously addressed the Conservative party conference with a plan to legalise gay marriage before 2015. "Yes, it's about equality," he said, "but it's also about something else: commitment. Conservatives believe in the ties that bind us... So I don't support gay marriage despite being a Conservative. I support gay marriage because I'm a Conservative."

Cameron's take on the issue is unusual. Supporters of gay marriage usually argue from a liberal perspective. They see the ability to marry as a basic civil and human right, and are deeply disturbed by injustice done in the name of morality. Conservatives see the issue through a different moral lens. Over 70 per cent of US conservatives still oppose gay marriage, often citing the affront to social stability, tradition and the sanctity of marriage between a man and a woman.

Like abortion, gay marriage is one of those hot-button issues in the culture war between liberals and conservatives. Why do people disagree so fundamentally, and why are they so convinced morality is on their side?

Over the past few years, psychological research has begun to offer answers to this question, and a surprising number of them boil down to disgust.

In 2008, a team led by Simone Schnall of the University of Plymouth, UK, found that inducing feelings of disgust - by a flatulent smell, dirty surroundings or a movie clip of a filthy toilet - increased the severity of people's judgements about a range of morally suspect actions, from pilfering cash from a found wallet to eating a dead dog (Personality and Social Psychology Bulletin, vol 34, p 1096).

This effect has since been confirmed and extended. A group led by Kendall Eskine at the City University of New York found that the effects of disgust on moral judgements were particularly strong for those on the political right (Psychological Science, vol 22, p 295). And several studies led by Yoel Inbar of Tilburg University in the Netherlands have found that conservatives are more easily disgusted (Cognition & Emotion, vol 23, p 714).

This year, Inbar's team found that exposure to disgusting smells can amplify negative attitudes toward gay men in both liberals and conservatives (Emotion, vol 12, p 23). Interestingly, it had no effect on attitudes towards other social minorities such as lesbians, African-Americans or the elderly.

So there seems to be an intuitive link between disgust and moral judgement, and this link seems to be much stronger for conservatives than for liberals.

This, we believe, explains some of the differences in opinion on gay marriage. In short, conservatives are more likely to find homosexuality disgusting and therefore morally unacceptable; liberals might feel some disgust at the idea of gay sex but consciously reject it as a basis for moral opinion.

Other research has found that liberals tend to see moral issues in terms of individual suffering or unfairness, whereas conservatives have more group-level concerns, such as loyalty, patriotism and respect for authority and tradition. Across dozens of countries, liberals are more morally offended by the idea of kicking a dog or cheating at cards than by ideas of betraying their family, cursing their parents, or doing harmless-yet-disgusting things like urinating in public. Conservatives find all of these equally repugnant.

All this research not only shows why disagreements about gay marriage are so intractable, it also suggests ways that those who support the idea can get through to people morally opposed to it. Because liberal supporters of gay marriage see morality as a matter of minimising harm and unfairness, these are the terms they exclusively use in their arguments about why banning it is wrong. Conservatives might agree about the importance of equality, but are more likely to have an intuitive aversion to homosexuals, seeing them as out-group members trying to infiltrate the sacred in-group institution of marriage, flaunting their disrespect for traditional gender roles, and doing what they see as disgusting things to each other in the bedroom.

In our home state of Missouri, a flyer sent out by the Republican party included images of what would happen if liberals came to power: immigrants flooding in, the Bible being banned and gay men kissing in public. Ridiculous as this seems (especially to liberals), such moral button-pushing has been an effective strategy for the right, in part because those on the left aren't addressing the deeply held moral intuitions triggered by such caricatures.

Again, difficult as it may be for liberals, they should follow Cameron's lead. By explicitly associating gay marriage with conservative values, Cameron went beyond simply repeating that banning it wasn't fair.

If opponents can be persuaded that homosexuals are crucial members of the national in-group (often fighting for their country, for example), that legalising gay marriage would be part of a rich tradition of expanding civil liberties, and that gay marriage is more about love and commitment than sex, then marriage equality could be achieved much more quickly.

Sarah Estes is a science writer based in Los Angeles.

Jesse Graham is assistant professor of psychology at the University of Southern California

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