Legalising same-sex marriage reduces prejudice against gay people, according to new research.
The study of evolving attitudes toward same sex marriages in the United States found that legalisation had a “significant” impact on reducing anti-gay bias.
In states where prejudice against same-sex marriage was in decline already, the study found legalising it doubled the rate of the decline.
But in states where the legalisation of same-sex marriage was rejected, anti-gay feelings increased after the Supreme Court ruled it was legal country-wide.
Researchers say the findings provide evidence that public policy can shape social norms and change individuals’ attitudes.
The study, by researchers from McGill University in Canada, focused on US States as they legalised gay marriage and the subsequent changes in attitudes.
In 2004, Massachusetts became the first US state to legalise same-sex marriage.
In the following years, 34 other states and Washington DC would follow suit before the Supreme Court ultimately ruled, in June 2015, that same-sex couples could marry nationwide.
Since then, polls have suggested that support for same-sex marriage has steadily increased.
Study senior author Professor Eric Hehman, who specialises in how individuals perceive one another and how stereotypes and biases influence behaviour, set out to measure whether and how state legislation had an impact on anti-gay bias.
He said: “The idea that norms shape attitudes has been around in social psychology for many years.
“We wanted to measure if laws and policies can also act as norms and potentially change deeply rooted biases.”
Since same-sex marriage was legalised in different states over the course of 11 years, Hehman’s team was able to map trends in anti-gay bias during this period.
By analysing responses at Project Implicit – a website launched in 2002 that measures biases of respondents – Eugene Ofosu, a graduate student working with Prof Hehman, examined changing regional anti-gay biases of about one million respondents over a 12-year period.
The researchers compared these trends before and after state-level legalisation of gay marriage in each state.
Though implicit and explicit bias against the gay community was decreasing or stable prior to same-sex marriage legalisation, the researchers found that legislation supportive of this marginalised population caused anti-gay bias to decline at roughly double the previous rate.
In the 15 states that did not pass same-sex marriage legalisation locally by contrast, Hehman found a “backlash effect.”
In those states, anti-gay bias increased in the immediate aftermath of the Supreme Court ruling making gay marriage legal nation-wide.
Prof Hehman said that one possibility is that even though attitudes were shifting toward more acceptance of same-sex marriage, a tipping point of support had not yet been reached in those states for the majority to accept the federal ruling.
The study also suggested that attitudes and legislation may be mutually reinforcing – evolving attitudes toward same-sex marriage may have been the force behind both state and federal legalisation.
Prof Hehman said: “In other words, representative governments can contribute to and/or intensify change in the attitude of citizens by passing legislation.
“We have some evidence that the laws caused this changed in bias, but it is possible the effect goes in both directions.”
The findings were published in Proceedings of the National Academy of Sciences (PNAS).