It often said that people who are loudest in their condemnations of homosexuality are probably hiding their own homosexuality. Anecdotes aren't data, however, so no manner how many homophobic bigots come out of the closet that wouldn't prove that there is a link between homophobia and repressed homosexuality.
Fortunately, we do have data -- real scientific data. There have been scientific studies which reveal strong links between being homophobic and harboring repressed homosexual urges or desires. This doesn't mean that every homophobic bigot is trying to repressed their own homosexuality, but it does make it a legitimate possibility and might be more common than is currently believed.
One of the most important lines of work in this area dates back to a 1996 article published in The Journal of Abnormal Psychology. In this empirical paper, researchers Henry Adams, Lester Wright, Jr., and Bethany Lohr from the University of Georgia report evidence that homophobic young males may secretly have gay urges.
In this study, 64 self-reported straight males with a mean age of 20.3 years were divided into two groups ("non-homophobic men" and "homophobic men") on the basis of their scores on a questionnaire measure of aversion to gay males. Here, homophobia was operationally defined as the degree of "dread" experienced when placed in close quarters with a homosexual--basically, how comfortable or uncomfortable the person was in interacting with gay people. (There is debate in the clinical literature about the semantics of this term, with some scholars introducing other constructs such as "homonegativism" to underscore the more cognitive nature of some people's antigay stance.)
Each participant then agreed to attach a penile plethysmograph to his, well, "lesser self." According to the authors, this plethysmograph device is "a mercury-in-rubber circumferential strain gauge used to measure erectile responses to sexual stimuli. When attached, changes in the circumference of the penis cause changes in the electrical resistance of the mercury column." Previous research with this apparatus (the plethsymograph, not the penis--well, actually both) confirmed that significant changes in circumference occur only during sexual stimulation and sleep.
Next, the participants were placed in a private chamber and presented with three 4-minute segments of graphic pornography. The three video snippets represented straight porn (scenes of fellatio and vaginal intercourse), lesbian porn (scenes of cunnilingus or tribadism), and gay male porn (scenes of fellatio and anal intercourse). Following each randomly ordered video presentation, the participant rated how sexually aroused he felt and also his degree of penile erection. Can you guess the results?
Both groups--non-homophobic and homophobic men--showed significant engorgement to the straight and lesbian porn and their subjective ratings of arousal matched their penile plethsymograph measure for these two types of video. However, as predicted, only the homophobic men showed a significant increase in penile circumference in response to the gay male porn: specifically, 26 percent of these homophobic men showed "moderate tumescence" (6-12 mm) to this video and 54 percent showed "definite tumescence" (more than 12 mm). (In contrast, for the non-homophobic men, these percentages were 10 and 24, respectively.) Furthermore, the homophobic men significantly underestimated their degree of sexual arousal to the gay male porn.
Source: Scientific American
There have been some attempts at alternative explanations for this data but the author is able to argue that they aren't very convincing. It's hard to find fault in the reasoning here: if you find something attractive which you also believe is evil or disgusting, then not only will you repress it but you'll act to eliminate it from view. You can't be tempted by something you both love and hate if you can't see or hear it anymore.
This connection between homophobia and violence is extremely disturbing. Being homophobic isn't just linked to repressed homosexual desires, it's also linked to an increased willingness to use violence against people for no other reason than that they are gay:
Some of the most startling data I've come across lately involve a 1998 survey of 500 straight males in the San Francisco, California area. Half of these men said they had acted aggressively in some way against homosexuals (and these were just the ones who admitted to such acts). And a third of those who hadn't struck out in this manner against gay people said that they would assault or harass a "homosexual who made a pass at them." If you missed the irony, this was in San Francisco--arguably one of the most "gay-friendly" places in the world!
In one experiment described by the author, homophobic men delivered electrical shocks of greater intensity and longer duration when they thought the victim was a gay man than when they thought it was a straight man -- and this was simply "punishment" for answering a question wrong. The homophobic men essentially lashed out against gay men they didn't know and had no connection to. The fact that they were gay was the sole reason for hurting them.
When it comes to homosexuality, the conservative Christian motto is: love the sin, hate the sinner.