Good news: This exact study was carried out in the mid-1990s at the University of Georgia. Using penile plethysmography, researchers compared the erectile responses of 35 homophobes and 29 non-homophobes to pornographic films in various gender configurations. All the men were clearly aroused by the lesbian and straight porn, but their sexual responses differed when it came to the gay clips. Around three-quarters of the guys in the homophobic group experienced some engorgement—not nearly as much as they'd had watching other clips, but enough to be labeled as either "moderately" or "definitely tumescent" by the researchers. In the non-homophobic group, the proportion was just one-third.
But even these penis-based findings won't tell us very much about human nature. The results haven't been formally replicated by another lab since they were published, and as the Georgia team concedes in its original paper, there's a long history of research demonstrating that anxiety itself can produce sexual arousal. A 1977 study, for example, measured vaginal blood volume in women as they watched erotic film clips, some after having viewed a graphic depiction of an auto accident. Women in the crash group became aroused more rapidly than the others. More recent work from a group at the University of Texas, Austin, finds that moderately anxious women have a much higher sexual response than either low-anxiety or high-anxiety women. The UT researchers propose that activation of the sympathetic nervous system (the one we use for fight-or-flight responses) plays into our erotic behaviors.
Similar research has shown that men develop larger erections when they're afraid of receiving an electric shock. And a classic study from 1943 confirmed the rather unsurprising fact that at least half of all adolescent boys can develop erections from nonsexual experiences, especially when those experiences inspire excitement, fear, or another strong emotion. (Among the examples given in that paper: "Being late to school," "Fast elevator rides," "Finding money," and "Long flight of stairs.")
So the gay-versus-straight porn plethysmography study suffers from the same problem as the one that was just written up in the Times: The self-proclaimed homophobes might have been showing their anxiety, as opposed to their lust.
The irony to all this is that we don't need penile circumference and reaction-time measures to tell us what we already know: Of course some homophobes are gay! The folk wisdom about people who protest too much comes out of a massive data set of social experiences and communal observations. (As the Times op-ed point outs, Ted Haggard has acknowledged that his denunciations of homosexuality may have had something to do with his own yearnings.) What’s interesting is the enthusiasm with which this seemingly self-evident news has been received. The Times op-ed is one of the newspaper's most emailed and most viewed pages since it was posted online. Why? Because Times readers want to spread the word: If you're campaigning against the gay “lifestyle,” then you're probably pretty gay yourself. I bet they have a secret urge to scare the homophobes into shutting up. Give me a stopwatch and some wedding-cake figurines, and I’ll prove it.