Massive demonstrations are set for Sunday across France by opponents of a new government proposal to legalize gay marriage. The protesters say they have nothing against homosexuals, while gay rights activists denounce the homophobic tendencies of opponents of same-sex marriage. Social psychologist Laurent Bègue, author of “Right and Wrong Psychology,” is convinced that the line between homophobia and homosexuality is thin.

PARIS - In Sam Mendes’ film “American Beauty,” a former US marine and convinced conservative expresses his disgust with homosexuality (and humiliation) by ultimately shooting his neighbor – Lester Burnham, played by Kevin Spacey -- who had refused his sexual advances. This strange and tragic paradox may not remain pure cinematographic fantasy since, statistically, where you find communities that can be usually affiliated with homophobia (not necessarily homophobes), the violence of the words don't always correspond with the needs of the flesh.

Pope Benedict XVI was forced to remove German Bishop Walter Mixa, a man who had repeatedly pronounced violent homophobic discourses, even as he was himself homosexual according to the weekly “Der Spiegel.” There are other similar examples, such as American televangelist Ted Haggard.

How to test the theory?

To be taken seriously, the possible link between homophobia and homosexuality needs more substance than some anecdotes and an Oscar-winning movie. To put to the test the latent Freudian theory that repressed homosexual urges lead to homophobia, some mischievous American researchers from the University of Georgia carried out an unusual experiment.

They invented the instrument they dubbed the “plethysmograph,” which is actually a plastic band composed of mercury, meant to measure penis size during erections, that they believed could bring a touch of quantatative modernity to this old idea.

This rather unusual experiment proved that whenever a homosexual scene was shown to a professed homophobic male audience (determined a few days beforehand thanks to a questionnaire), these people had a higher tendency to have an erection than the others.

The numbers revealed that 80% of the homophobes had an increase in penis size compared to 34% of the non-homophobic population. The whole group’s reaction to heterosexual films was exactly the same, though. When the participants were asked if, according to them, they felt turned on by the scenes, the homophobes were the only ones to underestimate their effect on them.

This experiment on repressed homosexual tendencies needs to be renewed to end the controversy it already provoked, but it gives us nonetheless something to think about given how “hot” the topic is right now.

*The writer is a professor in social psychology and author of “Right and Wrong Psychology”