Actual researchers, writing in the Journal of Health Economics, have found that tolerance of homosexualtiy and the legalization of same-sex marriage actually correlates with less risky sexual behavior and, consequently, fewer HIV cases.
To those in the field of public health, to say that tolerance decreases risky sexual health behaviors is not a Startling Revelation. While some folks believe slogans like "abstinence only" or "just don't act on your gay impulses" to be ideal messages to prevent social ills like teen pregnancy or HIV from happening, these messages deny the reality that humans are sexual beings and, therefore, will seek out sex albeit, with the help of such messaging, with more shame and less health information.
That, in a nutshell, is one explanation as to why greater tolerance for homosexuality could correlate with less risky sexual behavior. Indeed, that was one of two hypotheses the researchers tested. In their words:
"An intolerant social environment may drive homosexual behavior underground. This type of risky behavior is characterized by anonymous encounters with high-risk individuals in secret, socially disconnected venues. Social acceptance of gays may consequently induce gay men to interact in open and socially mediated venues associated with less risky sexual behaviors."
Their second hypothesis was that tolerance could increase the number of "low-risk men coming out of the closet and entering the pool of sexual partners."
The researcers also considered, controlled for, and ultimately rejected, alternative hypotheses. For instance, it could be that HIV affects tolerance so that when HIV rates rise (or fall), tolerance of gays falls (or rises). They rejected this argument, noting that HIV is "not observable." That is, even people who have it don't always know they have it and reported cases of HIV/AIDS reflect the HIV rate years earlier, not for a current year.
They also considered whether changing behavioral norms in the gay community might increase tolerance and, in turn, reduce HIV. The researchers rejected this alternative hypothesis, noting that gays are an "extreme minority," making it unlikely that the general population would even be aware of changes in behavioral norms.
After controlling for other possible causal mechanisms, the researchers found that "tolerance has a negative effect on the male-to-male HIV rate in all the reported regressions, and the effect is statistically significant in four out of five regressions." They also found that tolerance was unrelated to the hemophilia HIV rate and gonorrhea rates (a disease characterized by male-to-female transmittal). However, they also found that tolerance does have a negative association with syphilis rates. As syphilis is also characterized by male-to-male transmission, this finding strengthens the causal relationship between tolerance and risky sexual behavior.
Finally, the researchers found that tolerance also has a negative association with heterosexual HIV rates, arguing that tolerance "may affect the spread of HIV among heterosexuals by alterting the behavior of bisexuals." That is, when society is more tolerant of homosexuality, bisexuals- like gays- may be less likely to be driven underground to engage in high-risk sexual behavior and it could introduce more low-risk men coming out as bisexual and entering the sex pool.
It's an interesting study, and perhaps one to add to the pile of evidence in support of Not Letting Homobigots Make Health Policy Decisions (or any decisions affecting LGBT rights, really).