The same-sex marriage debate in Australia was always bound to be divisive and emotive. And as a public vote on whether it should be legalised nears, the role of advocacy advertisements will become increasingly important in swaying the opinion of undecided voters.

While polls show strong support for marriage equality at present, the history of widespread advocacy campaigns shows that the “No” campaign has many unfair advantages – especially when it uses ads to make its point.

Further reading: Revealed: who supports marriage equality in Australia – and who doesn’t

The No campaign’s natural advantage

The efficacy of both the “Yes” and “No” arguments can be related to Mill’s “harm principle”: one side believes the only harm being done is to those who happen to be attracted to those of the same sex; the other side believes harm is being done to religious and moral values. How they present these ideas will dramatically affect the outcome of the vote.

However, the No campaign has distinct advantages when it advertises. These primarily relate to status-quo bias. Research shows that political actors often have an aversion to change, and will disproportionately focus on perceived losses relative to perceived gains.

As such, advocacy campaigns that focus on losses tend to do better than those focused on gains. On same-sex marriage, the gain is clear for some (such as those seeking to marry, and the rights this affords), but it is more reliant on more abstract notions like “fairness” for those not directly affected.

To that end, a campaign that suggests same-sex marriage will somehow erode many people’s rights (or those of their children) has an advantage over a campaign focused on establishing new rights.

Further reading: Without proper protections, same-sex marriage will discriminate against conscientious objectors

The No campaign’s second advantage comes with its ability to muddy the waters and associate as many negatives with same-sex marriage as it can. Again, this uses status-quo bias: when in doubt, people typically vote no.

And “facts” play an almost negligible role in changing voter behaviour in the face of strong emotionally based arguments.

The ad campaigns so far

So far, the ads for and against same-sex marriage have been intelligently made.

Polls have consistently shown that as the religiosity of Australians has declined, support for gay rights has grown. This bodes poorly for the No campaign, and it knows it. As a result, the Australian Christian Lobby has focused more on the idea that same-sex marriage will lead to a sort of social, moral decline.

Its ad cites no evidence for the assertions in it, but facts and evidence are less relevant in political advertising than many might like to think.

It’s a smart ad: it builds an emotional connection with traditional family-oriented voters, based on fear. Importantly, it sows doubt in those it connects with, which can be hard to overcome.

Another ad designed to air on Father’s Day was blocked by Free TV Australia, which considered the ad political. The group behind it, Dads4Kids, neglected to attach an identification tag, which would have resolved the issue.

The group denied the ad was either political or related to the marriage vote. But two lines in the 60-second spot appear designed for the debate: first, “Your mummy and I are a perfect team”, then “I can’t wait to … watch as you put on a wedding ring”. These are presented as positive messages, but reinforce existing ideals of parenting as between men and women.

These kinds of ads may be used again, but are less effective for the No campaign than the more overtly stress- or fear-inducing ones.

Experts assert there is no evidence to support the No campaign’s assertions. Its messaging is, in that strict sense, irrational.

But that’s the point: muddying the waters in advocacy advertising plays on the unquestioning parts of the brain. Fear of the unknown and unknowable can be baseless – even silly – but it works.

When Yes Equality launched its first TV ad, it was defensive, and focused on the evidence problems with the No ads.

The latest ad from the Yes campaign doesn’t give viewers the time to build any connection: there are too many faces, too much going on.

Debunking and clearing up confusion is important, as is mobilising voters, but the most successful campaigns focus more on establishing emotive-empathetic links with viewers than rational ones

Such campaigns usually rely on stress or anger. The US campaign against “Hillarycare” did it in 1993; when unions fought the WorkChoices legislation, they did it too; and the mining industry did it in its battle against the Rudd-Gillard mining taxes in 2010.

Giving the same-sex marriage debate relatable, likeable faces, and building emotional narratives, will be critical to countering the fear-based charge of the “No” ads. This is especially the case if the campaign maintains or increases its advertising spending.

Lessons from Ireland

Ireland’s 2015 referendum on same-sex marriage offers compelling – if not completely analogous – examples of what might happen in Australia.

Ireland voted in favour of same-sex marriage, 62% to 38%. This was well down from pre-referendum opinion polls, where support was as high as 76%. Polling shows Australians’ support for marriage equality is similarly strong — as high as 76% – and it’s likely a charged debate will bring a similar drop.

However, there is a key difference. In Ireland, political ads are banned on broadcast media – so, no TV spots, nor radio. Australia has no such prohibition.

The complexity of an issue like same-sex marriage (or almost any political issue) is not well distilled into 30-second audio-visual pitches. Instead of through ads, the Irish debate largely took place on panel discussions, in parliament, and in public and private places around the country.

The closest ads Ireland ran to Australia’s TV spots were internet-based, such as those made by the Iona Institute and Mothers and Fathers Matter. These pushed the idea that both a mother and a father were necessary or ideal for bringing up children.

Otherwise, the ads were made for billboards, newspapers and the internet, but their impact was likely to be lower than if TV spots were used. Internet ads generally have lower saturation and reach fewer demographics (including older voters, who are more likely to resist same-sex marriage).

And static, image-based ads don’t have the same efficacy as TV ones – especially in terms of emotive reactions, which lend themselves more to irrational associations.

What to expect as the vote nears

Ireland’s experience shows that even where ads are kept from broadcast media, there can be a dramatic drop in support for same-sex marriage after a prolonged, divisive debate. But throwing well-made TV and radio ads into the mix may well prove a critical distinction between Australia and Ireland.

The No campaign will continue to draw on as many negative associations as possible, especially related to children. Its campaign has been significantly dependent on fear, and shows no indication of changing.

Once the vote is properly underway, the intensity of the ads is likely to increase. Without an adequate counter from the Yes campaign – especially one offering more emotionally compelling messages – the advantages of the No campaign are likely to narrow the polling gap significantly.