When Melissa, an administrative assistant in a law firm who’s in her 20s, met an older woman named Lisa a few years ago, it was love at first sight. The two have been in a relationship ever since but know that marriage is out of the picture. And it’s not because they are lesbian. It’s because they are mother and daughter.

Incest is still society’s deepest-rooted sexual taboo, mainly because the word is so often associated with rape and inbreeding. But consensual incest exists, and cases like Melissa’s — who discovered Lisa, a personal trainer, was her biological mother only after the West Coasters had started dating — pose their own host of ethical dilemmas, including some we may finally be ready to discuss.

It wasn’t that long ago when homosexuality and sadomasochism were also considered taboo. These days, though, Hollywood’s offerings are packed with homoerotic imagery and commuters are happy to crack open a copy of Fifty Shades of Grey on the morning train to the office. So if pop culture is anything to go by (and when isn’t it?), there are some signs that romantic love between family members is slowly becoming less socially outrageous. Look no further than HBO’s Game of Thrones — which explicitly portrays sex between a brother and sister — or scenes of a mother and son going at it in Boardwalk Empire.

Then there’s the growing demand, adult industry experts say, for incest porn — aka “fauxcest.” According to the site Pornhub, “step-mom” was the fourth-most searched term in 2014, while “step-sister” has climbed 53 places year on year to the 13th spot. “It would seem that lines around the incest taboo are shifting,” says Dr. Chauntelle Tibbals, a sociologist and author of Exposure: A Sociologist Explores Sex, Society, and Adult Entertainment.

We need to start asking if it’s OK to limit someone’s freedom just because we have a ‘yuck’ response to it. Debra Lieberman, assistant professor, University of California, Santa Barbara

Of course, there are plenty of reasons why the word incest itself has such dark connotations. About 5 percent of rapes in the U.S. take place within the family, and determining what is consensual in a familial environment is extremely difficult. In many cases, experts warn, incest destroys families and hurts people’s ability to trust others and form healthy relationships. So while consensual incest does exist, “legalizing it would be too risky because it may incentivize it,” says Dr. Karin Meiselman, a psychologist who specializes in treating incest cases.

For people like Sarah, however, the social stigma feels grossly exaggerated. The 27-year-old journalist from London recalls with a smile the time she and her cousin had sex after a birthday party. “Nothing about it felt wrong,” she says. “We were adults, we both wanted it and we are still friends. What’s wrong with that?”

Science doesn’t have a clear answer. Humans are wired to develop a sexual aversion toward close family members to avoid inbreeding, some research shows, but that mechanism is usually triggered by growing up together. So when family members don’t meet until they’re adults, attraction is actually pretty common. “Imagine meeting someone who has your exact predilection for spicy food or music, which is likely since you share that much genetic material,” explains Debra Lieberman, an assistant professor at the University of California, Santa Barbara who has done extensive research on incest aversion. “We need to start asking if it’s OK to limit someone’s freedom just because we have a ‘yuck’ response to it.”

The German Ethics Council agrees. Last year, this independent body of experts called for an end to the criminalization of incest between siblings and argued that, even if rare (it touches only 5 percent of siblings), it isn’t appropriate for criminal law to preserve a social taboo. France will soon add the word “incest” back into its penal code to label sexual abuse within the family (French legislators had stopped using the term two centuries ago), but the decision doesn’t change any of the pre-existing laws condemning rape. Consensual incest is still legal in the land of baguettes.

Governments have long used two arguments to criminalize consensual incest — risk of inbreeding and damage to the family — but societal changes may be chipping away at both of these stances. While couples who are close relatives do have a higher chance of having children with severe birth defects, today there are many effective ways to avoid pregnancies, or to get pregnant using a third person’s genetic material. The need to protect the traditional family structure may also become less relevant as society changes. When one case of consensual incest between a stepfather and stepdaughter was brought to the Supreme Court in 2007, the judges ruled it should remain illegal because it harmed the family. But J. Dean Carro, the lawyer who defended the incestuous couple says, “We were ahead of our time, but legalization will happen because such cases will become more common.”