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There was once a time when deciding not to have children automatically made you a social pariah. And even as an increasing number of people are choosing not to become parents, the social bias against childfree adults persists.

Birth rates among 20-something women have declined steeply as millennials delay marriage and having kids in order to focus on things like education, career, personal growth and financial stability. Many others aren’t having children at all, and the number of women who have chosen to forgo motherhood altogether has doubled since 1970.

Yet many people still consider the decision to forgo parenthood as not only abnormal and surprising, but also morally wrong, suggests new research from Indiana University-Purdue University.

The findings, published in the March issue of Sex Roles: A Journal of Research, show that most people view parenthood as a moral imperative for men and women.

For the study, 204 psychology students at a Midwestern university read a short passage about a married adult and then rated their feelings toward the person and their perception of the person’s level of psychological fulfillment. The only details in the passages that changed were the character’s gender and whether they had chosen to have kids.

Childfree men and women were consistently viewed as being less personally fulfilled than those who had two children. This is likely due to the fact that the participants reported significantly greater feelings of moral outrage ― including anger, disgust and disapproval ― toward the voluntarily childless people.

Perceiving the childfree people as less fulfilled acts as a way of “punishing” them for violating what’s often considered to be both a social norm and a moral imperative, according to study author Dr. Leslie Ashburn-Nardo.

Parenthood is a cultural norm ― and as with other norms, violations are not looked upon kindly. Research has shown that people who diverge from social role expectations often face backlash from other members of society for defying the unwritten social contract.

“People who violate social role expectations based on widely shared cultural stereotypes are subject to perceivers’ backlash.” - Dr. Leslie Ashburn-Nardo

“Through parents and peers, people learn that parenthood is both typical and expected,” Ashburn-Nardo wrote. “People who violate social role expectations based on widely shared cultural stereotypes are subject to perceivers’ backlash, such as social and economic sanctions and sabotage. This backlash is justified in the minds of perceivers because the targets are thought to have brought it upon themselves by not fulfilling their expected roles.”

Of course, the fact that childless women are widely discriminated against shouldn’t come as news to anyone. Childlessness has been described as the “final female taboo,” and women who choose not to become mothers are often considered selfish or career-obsessed. Women are still expected to conform to gender stereotypes and are criticized and punished when they don’t.

This enduring bias carries real repercussions. A 2011 study found that women without children suffer from poorer health, likely thanks to the enduring social stigma against childlessness. Childless people are also discriminated against in the workplace, being subject to less schedule flexibility and fewer tax breaks compared to their co-workers who are parents.

“Other research has linked moral outrage to discrimination and interpersonal mistreatment,” Ashburn-Nardo said in a statement. “It’s possible that, to the extent they evoke moral outrage, voluntarily child-free people suffer similar consequences. ... Exploring such outcomes for this demographic is the next step in my research.”