This article originally appeared on VICE US.

According to a study published in 2017 in Sex Roles, some people are outraged when complete strangers decide not to have children.

Since the 1970s, the percentage of younger women remaining childless has been on the rise, reports a Pew Research study. In fact, a growing number of couples are choosing small dogs over small humans. But past studies have shown that men and women who choose to be kid-free are often perceived negatively by others. Leslie Ashburn-Nardo, an associate professor of psychology at Indiana University-Purdue University Indianapolis, decided to investigate why these perceptions continue to exist, even as birthrates fall in the US.

Ashburn-Nardo and her team recruited 197 undergraduate psychology students to participate in the study. After being told the experiment had to do with people's sense of intuition and how accurately they can predict the future, they were given one of four versions of an anecdote about a married adult's decision to have children, with variables accounting for gender and whether they had zero or two kids. Participants were then asked to rate how psychologically fulfilled they thought the subject was. In another set of questions, researchers also gleaned if and to what extent participants felt disapproval, angry, outraged, annoyed, and disgusted toward the subject.

Not only did participants perceive the voluntarily childfree male and female subjects to be "significantly less psychologically fulfilled than targets with two children," Ashburn-Nardo notes, they also reported "significantly greater moral outrage" toward them. These findings offer evidence for the theory that parenthood is seen by some as a moral imperative: "In other words," the study states, "not having children is seen not only as atypical but also as wrong."

An interest in having children is "both a prescriptive and descriptive stereotype for men and women," the researcher writes. "[W]hen people violate strongly held norms and expectations such as those regarding parenthood and interest in children ... there are potentially serious consequences. ... 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."

Ashburb-Nardo draws attention to the fact that both men and women were stigmatised for choosing not to have kids—despite the fact that the conversation around reproductive rights and a woman's right to choose is so polarising. "I was somewhat surprised by this too," she tells Broadly, "but that was probably due to my own personal experiences as a woman. When I looked at the past literature, the few studies that included opportunities for participants to rate men without children yielded similar findings."

However, she continues, because "parenthood is seen as a moral imperative, something that we are supposed to do, this helps us understand why views about abortion are so strong."