To be a homophobe in 2014 is, increasingly, to find oneself on the fast track to social scorn. In an environment of growing acceptance, we condemn homophobic feelings, particularly in men, because we think they come from inside the individual and are thus his full responsibility. A man who says hateful things about gays is “backward.” He’s protecting his social status, or maybe he’s secretly gay himself. He needs to grow up or come out already.

However, the continued existence of homophobia—despite the obvious downsides—raises questions about its basic nature: Do psychological theories like those above really explain why gayness, specifically, evokes such fear, the kind that can sometimes even lead to violent speech and action? Do they account for why homophobia is such an easy bulwark against masculine insecurity? Why does coming out seem so impossible to some men? The only way to answer these questions is to stop thinking of homophobia as a personal choice and understand it as the inevitable and deliberate result of the culture in which American men are raised.

Clearly, men in America have grown up learning to be scared of gayness. But not only for the reasons we typically think—not only, in the end, because of religion, insecurity about their own sexuality, or a visceral aversion to other men’s penises. The truth is, they’re afraid because heterosexuality is so fragile.

Heterosexuality’s power lies in perception, not physical truth—as long as people think you’re exclusively attracted to the right gender, you’re golden. But perception is a precarious thing; a “zero-tolerance” policy has taught men that the way people think of them can change permanently with one slip, one little kiss or too-intimate friendship. And once lost, it can be nearly impossible to reclaim.

Put another way, the zero-tolerance rule means that if a man makes one “wrong” move—kisses another man in a moment of drunken fun, say—he is immediately assumed to be gay. Women have a certain amount of freedom to play with their sexuality (mostly because society has a hard time believing in lesbian sex at all). Male sexuality, on the other hand, is understood as unidirectional. Once young men realize they are gay, they become A Gay Person. We don’t hear about gay men discovering an interest in women later in life, and we rarely believe men when they say they are bisexual—the common, if erroneous, wisdom is that any man who says he is bi is really just gay and hasn’t admitted it yet.

The result of all this is that men are not allowed “complex” sexualities; once the presumption of straightness has been shattered, a dude is automatically gay. That narrative does not allow much freedom to explore even fleeting same-sex attractions without a permanent commitment. I knew a guy who, straight in high school, hooked up with dudes for the first semester of college. He was then in a monogamous relationship with a woman for the rest of college; in the weeks before graduation, I would still hear people express confusion about the existence of their relationship.

The zero-tolerance policy is legitimately scary, then, not just because it sticks you with a label, but also because it erases a lifetime of straightness. One semester of experimentation was worth more than every other hook-up and romance of this guy’s life—both before and afterward.

Read it at Slate.