North Carolina incited furor last week when it enacted a law banning transgender people from using public bathrooms that match their gender identity instead of their biology at birth. The ACLU filed suit on Monday, calling the law “unconstitutional”.

Tar Heel State lawmakers are just the latest proscribing transgender use of public facilities. Bills have been introduced in 16 state legislatures in the past four months alone, with calls for justice and access bumping noisily up against arguments about safety and privacy.

But transgender people are hardly the first to be embroiled in a very public bathroom brawl. The commode has been at the center of civil rights battles since the first modern public lavatory with flushing toilets opened in Victorian London.

Who were the interlopers back then? Women, of course, and they’re still fighting for “potty parity”. The US Congress, for example, has yet to pass the Restroom Gender Parity in Federal Buildings Act to make sure government buildings are built or leased with, at minimum, the same number of toilets in women’s restrooms as in men’s. Urinals are included in the count.

Public bathrooms are places 'where people’s level of discomfort is accentuated and magnified'

In the segregated south, Jim Crow laws banned black people from public “whites only” bathrooms until the 1960s, in perhaps the most elemental form of segregation. People with disabilities were not promised access to public lavatories until the Americans with Disabilities Act was signed into law by then-president George W Bush in 1990. Homeless people still struggle to find restrooms they are allowed to use.

Public bathrooms are “a flash point” because they are places “where people’s level of discomfort is accentuated and magnified in ways it isn’t in other places,” says Kathryn H Anthony, professor of architecture at the University of Illinois at Urbana-Champaign.

“People are afraid because they’re exposed,” says Anthony, author of Designing for Diversity: Gender, Race and Ethnicity in the Architectural Profession. “There’s a vulnerability we feel in public restrooms we don’t feel in other places.”

Why is this important? As she told the House committee on oversight and government reform in 2010, the average person uses a toilet six to eight times a day.

Toilets are everywhere. At least, they should be.

Marcel Duchamp turned a common urinal into a much-argued-over 1917 artwork called Fountain. Around half a century later, poet Marge Piercy blistered plumbing’s capitalist tendencies in To the Pay Toilet: “You strop my anger, especially/ when I find you in restaurant or bar/ and pay for the same liquid, coming and going.”

The politics of porcelain: Alfred Stieglitz’s photograph of Marcel Duchamp’s controversial work, The Fountain. Photograph: Alfred Stieglitz/AP

But it was Slovenian philosopher Slavoj Žižek who best encapsulated the politics of porcelain : “As soon as you flush the toilet, you’re right in the middle of ideology.”

No kidding. Just ask Bertie Brouhard or Kaeley Triller Haver.

Brouhard, 69, the self-proclaimed “largest, brightest, most Norwegian transgender Viking princess,” had gender reassignment surgery seven years ago. She has never been happier, she says. Or, sometimes, lonelier. Becoming your true self is a costly process.

A woman chased me into the ladies’ room and knocked on the stall ... I came out holding my driver’s license Bertie Brouhard

Her wife of nearly 40 years divorced her. She is only now working her way back into her eldest son’s life. All she wants to do is walk down the street like anyone else, use public facilities without harassment. Even here in famously liberal San Francisco, that is impossible.

“A woman chased me into the ladies’ room at city hall and knocked on the stall,” Brouhard recounted. “I came out holding my driver’s license. ‘May I see yours?’ At Macy’s. At Chase Bank. On Muni. I have story after story.”

She cannot understand why she cannot simply relieve herself in peace, although, she says, “the engineer in me would tell you that everything takes the path of least resistance. It’s so easy to pick on bathrooms. You pee differently than I do. It’s such a very basic human thing.”

But it’s only plumbing, Brouhard insists, “it’s not a sexual thing. It’s not a right-to-carry-a-gun issue. It’s not same-sex marriage. It’s not abortion. It’s going in to relieve yourself. Don’t carry it too far ... The bathroom is not a good place to start a fight.”

But Haver, who was sexually abused as a child, will not give up the fight to restrict access, although she concedes that she “would never in a million years have chosen this issue as my soapbox.”

The Gig Harbor, Washington, resident was recently hired as communications director for the Just Want Privacy Campaign, which has begun gathering petitions to put an initiative on the 8 November ballot in Washington state requiring, among other things, that school bathrooms and locker rooms be strictly segregated by anatomical sex.

The Washington state controversy began when the Human Rights Commission mandated in December that transgender people can use public restrooms consistent with their gender identities. Six bills were introduced in the state legislature to reverse that decision. All failed.

A supporter of Washington’s transgender friendly bathroom law, which has sparked debate. Photograph: Ted S. Warren/AP

Just Want Privacy began raising money and enlisting volunteers to change the Revised Code of Washington. The group wants to include admonitions such as this one: “The people find that requiring students to share restrooms, locker rooms, and changing areas with members of the opposite sex will create potential embarrassment, shame and psychological injury to students.”

One of my abusers’ pastimes was to watch me in the shower ... It doesn't mean I'm hateful. It’s crossing my line Kaeley Triller Haver

Haver said she was fired from her job at the YMCA of Pierce and Kitsap Counties when she refused to help the organization make its new policy, which allowed transgender people to use the locker room or restroom that matched their gender identity, palatable to members. The policy was enacted last April, before the state mandate.

“One of my abusers’ favorite pastimes was to watch me in the shower,” Haver said. “I can remember hearing him giggle. Even as an athlete, I would shower in my underwear. I never felt safe ... I’m sure there are survivors who are totally fine with these policies. I’m not. I’m not a bigot. It doesn’t mean I’m hateful. It’s crossing my line.”

Haver and others also argue that safety is a big concern; that men would dress up as women, demand entrance to women’s locker rooms and bathrooms and commit sexual assault on the unsuspecting.

“I caught multiple sex offenders in our facility over the years,” she said. “I knew that someone who wanted to exploit others would find loopholes.”

But a 2014 report by the US Department of Justice said transgender people are the ones most at risk of sexual assault. Citing recent studies of transgender experiences, the report said one in every two transgender individuals are sexually abused or assaulted during their lifetimes.

Chase B Strangio, an ACLU attorney involved in the North Carolina lawsuit filed Monday, said efforts to restrict restroom access are based on “two complete lies”.

One, he said, is that straight men will dress as women and attack women and children in women’s bathrooms. The other is that transgender people are “deviant and deceptive and are themselves fraudulent simply by existing”.

Public bathrooms are one of the few places where people have to share space with those who are different, he said, “a trans person, a gay person, a black person, someone who lives on the streets”.

There can be violence in public facilities, Strangio said, “but it is not increased when we extend nondiscrimination protection”.