My American friends frequently ask me why India's caste system, a pre-feudalistic division of labor that assigns one's line of work at birth, has persisted into the 21st century in defiance of every civilized notion of justice and equality. I thought I knew the answer: The need of the privileged upper castes for cheap labor to do their dirty work. But there is an even more tragic explanation that I discovered during a recent visit to New Delhi while talking to Maya, the dalit or untouchable—the lowest of the four castes—who has serviced my family for 35 years. Maya herself clings to her caste because it offers her the best possible life, even in modern India.

The puzzling thing about the caste system is that it has endured without any legal force backing it. Unlike slavery, under which whites actively relied on authorities to maintain their slave holdings, the caste system is an informal, self-perpetuating institution that has resisted half-a-century worth of (ham-handed) government efforts to eradicate it.

How? Consider Maya's story.

Maya assigned herself to our house in a small, gated community in West Delhi in 1977. We had no choice in the matter. If we wanted our trash picked, bathrooms scrubbed, and yards cleaned, Maya was it. Indians find dealing with other people's refuse not just unpleasant, but polluting. Hence only dalits, whose caste impels them to do this work, are willing to do it, something that both stigmatizes them and gives them a stranglehold on the market. And they have transformed this stranglehold into an ironclad cartel that closes the door on all alternatives for their customers.

When Maya got married at the age of 16, her father-in-law paid another dalit $20 for her wedding gift: the "rights" to service 10 houses in our neighborhood, including ours. Maya has no formal deed to these "rights" and no court would ever enforce them. Yet they are more inviolable than holy writ. Maya's fellow dalits, who own the "rights" to other houses, can't work in hers, just as she can't work in theirs.

Doing so, Maya insists, would be tantamount to theft that would invite a well-deserved beating and ostracism by the dalit community. No one would lift a finger to help a "poacher" in distress or attend her family functions like births, weddings, or funerals. She would become a pariah among pariahs.

This arrangement has given Maya a guaranteed monthly income of about $100 that, along with her husband's job as a "gofer" at a government lab, has helped her raise three children and build a modest house with a private bathroom, a prized feature among India's poor, in one of New Delhi's slums. But Maya's monopoly doesn't give her just money. It also hands her— and her fellow jamadarnis or sweepers— clout to resist the upper caste power structure, not always for noble reasons.

None of Maya's 10 employers dare challenge her work. Maya takes more days off for funerals every year than there are members in her extended family. Complaining, however, is not only pointless but perilous. It would result in stinking piles of garbage outside the complainer's home for days. Every time my mother, a stickler for spotlessness, has gotten into spats with Maya over her sketchy scrubbing habits, she has lost. One harsh word, and Maya simply boycotts our house until my mother goes, head hanging, to cajole her back. Nor is Maya the only jamadarni with an attitude. Nearly all of Delhi is carved up among Maya-style sweeper cartels and it is a rare house whose jamadarni is not a "big problem."

But Maya's clout comes at a huge personal price: It shuts the door on inter-caste acceptability. Segregation has loosened considerably among the first three castes. Intermingling and intermarriage, even among the highest brahmin and the relatively lower baniya (business) castes, is now common, especially in cities.

But dalits are allowed to socialize normally with other castes only if they give up trash-related work, although marriage remains taboo regardless. Otherwise, they are regarded as polluted and every interaction with upper caste folks becomes subject to an apartheid-like code.

Some of the homes where Maya works, for example, have separate entrances that allow her to access their bathrooms and collect their trash without having to set foot in the main house. Although the families have formed a genuine bond with her and treat her generously, plying her with lavish gifts on festivals, there are limits. They give her breakfast and lunch everyday, but in separate dishes reserved just for her. Sitting at their table and sharing a meal is out of the question. Not even my mother's driver who, though poorer than Maya, belongs to a higher caste (higher than my family's), would visit her home and accept a glass of water.

Maya is resigned to such discrimination, but not her oldest son, 36. He holds a government job and works as a sales representative for an Amway-style company and dreams big. He is embarrassed by his mother and often lies about her work to his customers for fear of being shunned. He claims he makes enough money to support Maya and wants her to quit, but she will have none of it. She fears destitution and poverty more, she says, than she craves social respectability. Her caste might be her shame, but it is also her safety net.

But the choice may not be hers much longer.

Upon retirement, she had planned to either pass her "business" to her children or sell it to another dalit for about $1,000. But about six months ago, local municipal authorities started dispatching vans, Western-style, to pick up trash from neighborhoods—the one service that had protected Maya from obsolescence in an age of sophisticated home-cleaning gadgetry.

Maya and her fellow dalits held demonstrations outside the municipal commissioner's office to stop the vans. The commissioner finally agreed to a compromise that lets Maya and her pals collect trash from individual homes and deposit it at one central spot from where the vans take it for disposal. But Maya realizes that this is a stopgap measure that won't last. "I got branded as polluted and became unfit for other jobs, for what?" she wept. "To build a business that has now turned to dust?"

Despite the financial loss, her son is pleased. He believes that this will finally force his siblings to develop skills for more respectable work instead of taking the easy way out and joining their mother. But Maya shakes her head at such bravado.

And she might be right. To be sure, post-liberalization, India has allowed the most dogged and determined dalits to escape their caste-assigned destiny, even creating the phenomenon of dalit millionaires. But for the vast majority, as Maya says, opportunities are better within the caste system than outside it.

When that changes, the system will die, but not until then.

Reason Foundation Senior Analyst Shikha Dalmia is a columnist at The Daily where a version of this column originally appeared