Just last week, the Journal of the American Medical Association released a study on how allowing for same-sex marriage resulted in fewer suicides of LGB adolescents (Raifman et al., 2017). The legal acknowledgment of same-sex marriage mitigated stigma behind gay, thereby reducing suicides in LGB adolescents by 14 percent. You might be thinking this is not an economic issue, but in fact, it is. When people say "children are the future," that means they are future employees in the workforce. Having happier and healthier children who grow up into being happier and healthier adults means a more vibrant workforce. This study is not the only one that shows results that can frame the issue in economic terms.
The United Nations economist Eric Lamontagne conservatively estimates that homophobia costs the global economy $119 billion annually, which is 0.1 percent of the world's GDP. World Bank consultant Mary Virginia Lee Badgett conducted a 2014 case study of homophobia in India. What she found was that homophobia could be bringing down India's GDP anywhere from 0.1 to 1.7 percent of its GDP (i.e., $2-31 billion). A 2014 report from the Williams Institute illustrates the strong correlation between homophobia and economic decline. While dated, a 2001 study from Canada shows that homophobia could be causing $1.9 to $8.1 billion of economic costs. The U.S. Senate Joint Economic Committee even makes the argument that workplace discrimination based on sexual orientation costs the economy.
Why does homophobia and anti-gay policy have such an effect on the economy? These policies come with enforcement costs, limiting job opportunities for LGB individuals, increased healthcare costs for LGB individuals that lowers life expectancy, societal stigma that makes it more difficult for LGB individuals to lead productive lives, the costs of increased likelihood of being victim of an anti-gay crime, the difficulties that a more homophobic society makes it for LGB individuals to form long-term relations, and incarceration costs for countries that have laws in which being gay or homosexual activity is punishable under the law. When you prevent productive people from participating in the labor force or make them less efficient then they could have been otherwise, that costs money.
Homophobia that translates into public policy is not just a civil rights violation or a severe moral shortcoming. Homophobia is also an unfortunate state of affairs that costs economies billions of dollars.