In his new book, Going Solo, New York University sociologist Eric Klinenberg argues that we’re poised to become a nation dominated by single people. Just 51 percent of American adults are married, according to recent census data, and more than a quarter of all U.S. households consist of only one person. Yet singles often don’t get a lot of love—and we’re not talking about their romantic lives.

Activists say that unmarried people are systematically discriminated against. They pay more for health and car insurance than married people do. They don’t get the same kind of tax breaks. Co-op boards, mortgage brokers, and landlords often pass them over. So do the employers with the power to promote them. “Singleism—stereotyping, stigmatizing, and discrimination against people who are single—is largely unrecognized and unchallenged,” says activist Bella DePaulo, the author of Singled Out.

DePaulo and other “singles’ rights” activists—like Sherri Langburt, who runs SingleEdition.com, a website that caters to the single community—are increasingly protesting what they say is a raw deal. If you’re picturing these fomenters as crazy-auntie types who eat a little tuna out of the can before giving it to their cats, think again. DePaulo, who got her Ph.D. from Harvard in 1979, is a psychology professor at the University of California, Santa Barbara. Langburt is a successful entrepreneur.

“The argument of advocates of same-sex marriage is, why do we have to be a certain kind of a couple in order to be treated fairly?” says DePaulo. “My argument is wider-reaching: why does anyone have to be part of any kind of couple to get the same federal benefits and protections as anyone else?” She adds: “People don’t notice singleism, and if their attention is called to it, they think there’s nothing wrong.” That’s why, for instance, car and health insurance companies get away with charging less for couples and families. “They can attract more business [that way],” DePaulo notes. In the process, they leave single people to essentially subsidize the benefit by paying more. “When married workers can add spouses to a health-care plan at a discount and single workers can’t add someone important to them, that’s discrimination,” says DePaulo.

The U.S. government not only turns a blind eye to the problem of “singleism,” but helps enforce it, activists say. Just look at Social Security. “A childless singleton can work side by side with a childless married person, doing the same job, for the same number of years, at the same level of accomplishment—and when the married person dies, that worker can leave his or her Social Security benefits to a spouse,” says DePaulo. “The single person’s benefits go back into the system.”

Unmarried people also lose out when it comes to taxes. “The U.S. tax system privileges married people in a variety of ways,” says Lily Kahng, a professor at Seattle University School of Law. In “One Is the Loneliest Number: The Single Taxpayer in a Joint Return World,” a paper recently published in the Hastings Law Journal, Kahng points out that married workers are able to transfer wealth and property to spouses—and others—tax-free, while the unmarried can’t; she concludes that the joint return penalizes single people and should be abolished.

“Married people had a supermajority of political power at the time the [current tax] rules were enacted,” Kahng notes. But today? “Single people continue to be marginalized even though they comprise close to half the adult U.S. population,” she says. That might have something to do with their lack of homogeneity as a group. Says Klinenberg, “There are so many different kinds of singles”—unmarried parents and the childless, those who cohabitate with partners and those who live alone, the young and the old—“that single people have had trouble organizing as a political bloc. But there are now so many ... it’s hard not to pay attention to them.”

That’s especially true given how much they contribute to society—more, activists argue, than married couples with families. “On average, singles have more disposable income,” Klinenberg says. “They're fueling urban economies that would be in much worse shape without them. And compared to married people, they’re more likely to spend time with neighbors, to participate in public events, and to volunteer.” (If any of that surprises you, think about how much less free time your married friends and colleagues have after their children are born.)

Singles may also be contributing more at the office, without being compensated for it, activists say. “Studies have shown that singles are often paid less than married people, even if they share the same title, responsibilities, and years of experience,” says Langburt. “And if you agree that time equals dollars, then it doesn’t stop there: there’s maternity leave, all the time off leading up to the pregnancy for doctors’ visits, and sick days.” On top of that, it’s de rigueur for companies to provide benefits for spouses and children—without providing equivalent perks for singles.

The prejudicial treatment can also be more blatant, activists say. An unmarried friend of Klinenberg’s with a high-power job at a social-justice organization was informed in no uncertain terms that she wouldn’t be getting a raise—because her married co-workers needed the money more than she did. “One of her partners told her, ‘We all have families to take care of, and you don’t,’” Klinenberg says. “These are people whose life work is social justice.”

Outside the office, the biased thinking persists, activists say. “For the single homeowner or property renter, discrimination is rampant, because the federal Fair Housing Act does not prohibit marital-status discrimination,” Langburt notes. “Not only do landlords discriminate again singles; so do real-estate and mortgage brokers. The problem is that it’s hard to pinpoint and track these incidents. Single women are the No. 1 home buyers in the country, but there’s still a silent stigma that these women don’t have money to qualify or that they will be a flight risk.”

Historically, governments have passed laws encouraging marriage and families in the hopes that doing so would decrease the likelihood that the state would need to care for abandoned children. But policies that benefit the married shouldn’t be substitutes for more universal social programs, says marriage historian Stephanie Coontz, the director of research and public education for the Council on Contemporary Families. “The penalties for being single in this country are worse than in Europe, where individuals have guaranteed access to health care, and they have options beyond a spouse’s death benefits for staying above the poverty line as they age.”

And let’s take a minute to talk about age. The Terman Life-Cycle Study, which started following 1,528 men and women in 1921 from age 11 for the duration of their lives, found that two groups of people lived the longest: those who got married and stayed married ... and those who stayed single.

Tell that to the insurance companies.