Today is Diwali, the biggest Hindu holiday, when believers celebrate the victory of good over evil. Usually, nothing dampens the Diwali spirit among observant Hindus, but this year there is a cloud hanging over some 30 million followers of Asaram Bapu, one of India's most popular Hindu gurus. This self-styled godman, a septuagenarian who has amassed a $1 billion empire by preaching the evils of sexual desire, is accused of raping the minor daughter of an ardent devotee.

Asaram is under arrest and, regardless of the final verdict, is finished. But he's not the first Hindu guru to go rogue, and he won't be the last. That's because to the extent that the loose and amorphous Hindu faith has avoided the tendency to militancy, internecine conflict and intolerance experienced by the more organized monotheistic faiths, it is at the price of opening itself to charlatans and cults.

A thousand gurus have always bloomed among Hindus. In the 1980s, there was Osho Rajneesh, whose fleet of Rolls Royces' and message of free love got him ejected from Oregon after a four-year stay. Among the new generation is the Hugging Amma, who has accumulated a net worth of about $250 million by jet setting around and giving 33 million hugs . Then there is Nirmal Baba, the TV phenom, who advises women to eat green—not red—chutney with samosas to get pregnant.

Bigger than all was Asaram. He combined a message that appealed to Hindus' puritanical sensibilities—renunciation of sensual pleasures and material comforts—with impressive oratory to generate a worldwide following. His devotees include a former prime minister, leading politicos, rich businessmen and professionals. The donations he raked in allowed him to erect 1,700 religious schools and 435 ashrams the world over.

The antics of gurus provide steady fodder for comedy in India. But Asaram's behavior was raising eyebrows even before the rape accusations. His anti-sex crusade had morphed from nuttiness (advising couples to avoid having sex on religious holidays) to extremism (demanding that Valentine's Day be replaced with Parent Worship Day).

Some details of Asaram's rise-and-fall are unique, but the basic plotline of a guru corrupted by power is as familiar as a B-grade Bollywood movie. The puzzle is why can't Hinduism, the world's oldest religion, rid itself of fake gurus?

Hinduism, unlike Christianity, is not an organized faith with settled dogmas, an established church and a priestly hierarchy handing down truths worked out top-down as in Catholicism. Nor does it prescribe a strict and elaborate code of law as Judaism's torah and Islam's sharia.

Rather, it is an open-ended faith that has a core goal—experiencing the God within and releasing oneself from the cycle of birth and rebirth — but no set prescription for achieving it. It simply calls upon believers to overcome their inner demons and find their own unique path to enlightenment. But a good guru, who has overcome the vices of ordinary mortals and reached a higher state of consciousness, can greatly accelerate the journey.

The effect of such radical openness, on the one had, is that Hinduism has produced an "absolutely staggering" body of "scientific, faith-based and experience-based knowledge," notes Josh Schrei, a religion writer. Diametrically opposed paths for achieving inner bliss have been explored: asceticism and materialism; intoxication and sobriety; sensuality and celibacy; solitude and communion.

On the other hand, Hinduism's spiritual laissez faire means that it lacks the inner resources of other religions for quality control. Unlike monotheistic faiths, Hinduism is not preoccupied with policing superstition, idolatry, and heresy. Literally anyone with a formula for enlightenment—and the charisma to sell it—can hang a shingle saying "guru inside" and wait for the flock to arrive. (This was perfectly captured by the recent documentary Kumare in which an Indian American born and raised in New York, moves to Arizona feigns a guru accent, invents some mumbo jumbo, and quickly acquires a devoted following.)

While there is no external hierarchy minding the gurus, there is an extreme internal hierarchy between the guru and the disciple. The guru's superior consciousness is neither visible nor describable. The only way for the faithful to reach it is by surrendering completely. Questioning the guru is not a sin, but it is counterproductive. "Faith is to believe what you do not see," explained Swami Chinmayananda, one of Hinduism's greatest theologians. "The reward of faith is to see what you believed."

Observers of Hinduism sometimes regard this total lack of oversight of gurus who can "simply make things up" to wield enormous powers over disciples as a defect. But that betrays a fundamental misunderstanding of the mind of its adherents: They are not gullible fools. They take a calculated risk that they intuitively feel is worth the spiritual payoff. Going down the wrong mystical path is an unavoidable hazard of their religion that they knowingly accept. They are no more blind or blinkered than lovers willing to repeatedly risk heartbreak to find a soul mate.

Thus, even as Asaram fades from the scene, others will emerge as surely as the holy Ganges will continue to flow downhill. All one can do, in keeping with the Hindu spirit, is to understand—and accept—that the good and the bad are often inextricably entwined.

Happy Diwali.

A version of this column originally appeared in The Times of London