Not just a theory...

You've probably heard people suggest that homophobia is an individual's attempt at hiding, denying, or repressing his or her own homosexual urges. In 1996, a group of psychologists at the University of Georgia decided to actually test it out.* They tested 64 white male volunteers using the Kinsey Scale, which shows how gay you are on a scale of 1 to 7 chose only those that identified as completely heterosexual in their arousal and experiences. They also tested the men with an Index of Homophobia, which rated them on how much anxiety they admitted to experiencing at the thought of being in a room with a group of gay people, among other things.

For step two of the experiment, they put each individual in a soundproof room alone where he attached an instrument to himself that measured changes in the circumference of his penis. In this room, with this instrument attached, they each man viewed three videos showing foreplay, oral sex, and anal and vaginal penetration. Each video was four minutes long, one showing heterosexual sex, one gay sex, and one lesbian sex. They used the lesbian sex video as a way to gauge the individual's level of homosexuality, as lesbian sex is known to be very arousing to straight men. They supposed that if the men were truly heterosexual and not just in the closet, they would show a high level of arousal after the lesbian video. Before starting a new video, the men's penises were allowed to return to their normal size. After each video, they were asked to record their level of psychological and physical arousal.

The study found that in the group of homophobic men, there was a significant increase in penis circumference after watching the homosexual sex video. In the nonhomophobic men, there was no increase after the homosexual sex video. They also noted that the homophobic men recorded low levels of arousal even though their erections indicated otherwise. Thus, they were not very willing to admit that they were turned on even though the data indicated that they were.

The study clearly shows that homophobia is a result of fear of one's own repressed homosexuality, at least in men. It's not just speculation any more.

*I'm pretty sure that the link to the actual article only works if you're on the Wheaton campus. If the link doesn't work, here's the citation:

Adams, H.E., Wright, L.W., Jr., and Lohr, B. "Is Homophobia Associated With Homosexual Arousal?" The Journal of Abnormal Psychology, 105(3), 440-445.