Let us suppose that there is a 'gay gene' - and i'm specifically talking about a gene which makes men tend to be gay, although the whole thing applies in reverse to women (ObAlx: DNA? DN-gay more like!). Given that carriers would tend not to have children, how would this gene be passed on from generation to generation? Partly, this may be due to positive effects of the gene on female reproductive fitness, but it may largely be due to the fact that historically, gay men had children in order to conform to repressively homophobic social norms.
So, now that social norms allow gay men to live outly, and not have children, there is a risk that the gay gene will be lost from the gene pool - and with it, a whole human subculture, and the majority of male fashion sense. Needless to say, this would be a disaster.
Step forward, the Gay Gamete Project: a concerted effort to get gay men to donate to sperm banks, in order that the Homo polone does not become extinct. Unfortunately, the regulations in the United States (and possibly other countries) expressly forbid sperm donation by gay men; therefore, the would-be conservationists must go undercover, lying about their sexuality to a government agency, and so committing sperm terrorism.
As far as i can tell, this is not a Greg Egan story.
I should add that the restriction on gay men donating sperm isn't actually part of a conspiracy to commit genocide on homosexuals; it's an (arguably overreactive) precaution against transferring HIV. This is also the reason why gay men can't give blood in the UK.