There are facts about circumcision—but you won’t find them easily on the Internet. Parents looking for straightforward evidence about benefits and risks are less likely to stumble across the Centers for Disease Control and Prevention than Intact America, which confronts viewers with a screaming, bloodied infant and demands that hospitals “stop experimenting on baby boys.” Just a quick Google search away lies the Circumcision Complex, a website that speculates that circumcision leads to Oedipus and castration complexes, to say nothing of the practice’s alleged brutal physiological harms. If you do locate the rare rational and informed circumcision article, you’ll be assaulted by a vitriolic mob of commenters accusing the author of encouraging “genital mutilation.”

How did it come to this? For years, circumcision was a private decision, encouraged by many doctors, practiced by most families (in America, at least), but little discussed in the public sphere. Yet in the past two decades, a fringe group of self-proclaimed “intactivists” has hijacked the conversation, dismissing science, slamming reason, and tossing splenetic accusations at anyone who dares question their conspiracy theory. For doctors, circumcision remains a complex, delicate issue; for researchers, it’s an effective tool in the fight for global public health. But to intactivists, none of that matters. The Internet is supposed to be a marketplace of ideas, where human reason leads the best ideas to triumph. There are plenty of other loud fringe groups that flood the Internet with false information, but none of them has been as successful as the intactivists at drowning out reasoned discourse. In the case of circumcision, the marketplace of ideas has been manipulated—and thanks to intactivists, the worst ideas have won out.

Like most fringe groups, the anti-circumcision faction is almost comically bizarre, peddling fabricated facts, self-pity, and paranoia. The intactivists also obsess about sex to an alarming degree. Still, some of their tactics are shrewd. The first rule of anti-circumcision activism, for instance, is to never, ever say circumcision: The movement prefers propaganda-style terms like male genital cutting and genital mutilation, the latter meant to invoke the odious practice of female genital mutilation. (Intactivists like to claim the two are equivalent, an utter falsity that is demeaning to victims of FGM.)

Anti-circumcision activists then deploy a two-pronged attack on some of humanity’s most persistent weaknesses: sexual insecurity and resentment of one’s parents. Your parents, you are told by the intactivists, mutilated you when you were a defenseless child, violating your human rights and your bodily integrity. Without your consent, they destroyed the most vital component of your penis, seriously reducing your sexual pleasure and permanently hobbling you with a maimed member. Anti-circumcision activists craft an almost cultic devotion to the mythical powers of the foreskin, claiming it is responsible for the majority of pleasure derived from any sexual encounter. Your foreskin, intactivists suggest, could have provided you with a life of satisfaction and joy. Without it, you are consigned to a pleasureless, colorless, possibly sexless existence.

Intactivists gain validity and a measure of mainstream acceptance through their sheer tenacity. Their most successful strategy is pure ubiquity, causing a casual observer to assume their strange fixations are widely accepted. Just check the comment section of any article pertaining to circumcision. When Slate’s Troy Patterson wrote a piece thoughtfully weighing circumcision’s pros and cons, he was attacked for supporting a “barbaric practice” of “mutilation” that “ought to be illegal.” A lighthearted Dear Prudence column suffered the same fate. Intactivists pummeled the Amazon rankings of a book about the history of AIDS that mentioned circumcision as a proven preventive measure. Check any Internet message board and you’ll find the same ideas peddled as unimpeachable fact: Circumcision is amputation, a brutally cruel and despicable form of abuse. It damages penises and violates human rights. And it irrevocably, undeniably ruins male sexuality for life.

The problem with these arguments is that they’re either entirely made up or thoroughly disproven. None of intactivists’ cornerstone beliefs are based in reality or science; rather, they’re founded in lore, devilishly clever sophistry dressed up as logic. The facts about circumcision may be hard to find on an Internet cluttered with casuistry—but they are there. And they prove that even as intactivists dominate the Internet, the real-world, fact-based consensus on circumcision is tipping in the opposite direction.

Take, for example, the key rallying cry of intactivists: That circumcision seriously reduces penis sensitivity and thus sexual pleasure. Study after study after study has proven this notion untrue. Some men circumcised as adults actually report an increase in sensitivity, while many report no appreciable difference; virtually none noted any notable decrease. Men circumcised as adults also almost universally report no adverse effect in overall sexual satisfaction following the procedure. (That fits with what my colleague Emily Bazelon found when she asked readers for their circumcision stories a few years ago.) And genital sensitivity in response to erotic stimulation is identical in circumcised and uncircumcised men. Don’t trust individual studies? A systematic review of all available data on circumcision came to the same conclusion. Intactivists, then, aren’t disputing a few flimsy studies: They’re contradicting an entire field of research.

So much for circumcision’s supposedly crippling effect on sexual pleasure. But what about its effect on health? Intactivists like to call circumcision “medically unnecessary.” In reality, however, circumcision is an extremely effective preventive measure against global disease. Circumcision lowers the risk of HIV acquisition in heterosexual men by about 60 to 70 percent. And circumcision reduces HIV risk over a man’s lifetime, unlike condoms, which must be used during each sexual encounter. It’s no wonder that the World Health Organization has pushed circumcision as a key tool in the fight against HIV.

But that’s not circumcision’s only benefit. The procedure also protects men against a variety of other STDs, significantly reducing their odds of contracting herpes and syphilis. Moreover, circumcision is highly effective in preventing transmission of HPV in men, which in turn reduces their risk of penile cancer. And circumcised men are far less likely to contract genital warts or develop urinary tract infections. Fewer circumcisions mean more STDs and infections—and billions more in health care spending.

As both a personal and public health matter, circumcision is clearly in men’s best interest. But intactivists, predictably, aren’t having any of it. Like anti-vaccine conspiracy theorists, anti-circumcision activists reject all science that doesn’t fit their angry, victimized orthodoxy. Does circumcision truly prevent HIV? Probably not, they say—but even if it did, it would ultimately increase risk of HIV by lulling men and women into a false sense of complacency. (Never mind that this is emphatically false.) Plus, they claim, circumcision has such high rates of complication that its benefits couldn’t possibly outweigh its drawbacks. (Again: simply incorrect.) Anyway, to intactivists, mutilation is mutilation; what does it matter if it’s for the greater good?

Thus far, intactivists’ ideological warfare has remained largely—though not entirely—toothless. Municipal ballot measures in America to ban circumcision have collapsed under the weight of their own weirdness; a German court’s anti-circumcision ruling was reversed by the legislature. On the Internet, though, it’s a different story. A generation of future doctors, scientists, and parents has now been exposed to a constant stream of acrimonious and unscientific lies about circumcision. Men across the world have been told their parents mutilated their genitals and ruined their sex lives. (Some even try to reverse the “damage”—for a price.) Conventional wisdom is starting to hold that even if circumcision is medically helpful, it’s also sexually harmful. Intactivists, in short, are winning the online battle. Is it only a matter of time until they win the greater war?