It’s not clear what, exactly, Lorie Smith’s problem is. The Colorado woman aspires to be a web designer; apparently, she’s also upset that gay people can get married. Smith is an evangelical Christian who says that her faith makes her object to same-sex marriage.

This wouldn’t be anyone’s problem, except that Smith lives in a state with a robust civil rights law, one that forbids business owners who make their services available to the public from discriminating. But Smith really wants to discriminate: she hopes to be able to turn away gay clients from her as-yet-hypothetical wedding website business; she wants to put a banner at the top of her business homepage proclaiming her unwillingness to design websites for gay weddings. The law would forbid this if she ever went into business, so she’s suing.

As of now, none of this has actually come up. At the time Smith filed her lawsuit, demanding an exemption to her state’s law, she didn’t even have a business with which to discriminate. The law has never been enforced against her; she’s never had the opportunity to discriminate that she so craves. It’s not clear, in other words, that she really has standing to sue – she’s never been forced to provide services to gay people, so, in legal parlance, there’s no “injury” to speak of. But Smith is an angry conservative, and she’s found some very well-funded lawyers from the Alliance Defending Freedom, a huge rightwing legal organization that has embarked on a nationwide campaign of lawsuits to erode civil rights protections for gay people.

The result is 303 Creative v Elenis, a case in which Smith argues that her religious convictions mean that she shouldn’t have to comply with a generally applicable civil rights law, and should be granted license to discriminate by her state. The US supreme court heard oral arguments on Monday, and the 6-3 conservative majority is certain to hand Smith a victory allowing her to deny service to clients based on sexual orientation.

A decision from the court is expected next summer. The question, as happens so often with this rabidly conservative court, is not who is going to win. That question was probably answered the moment the court agreed to hear the case, to the point that briefings and oral arguments in hot-button culture and identity cases like 303 Creative have been rendered largely moot.

The question, instead, is how far the court will go: how much the justices will unravel the anti-discrimination laws that govern public accommodations – that is, the laws that say that businesses which serve the public cannot deny service to people based on their identity – and how much discrimination, humiliation and bigotry in public life they will unleash upon gay Americans. The question is whether the speech that Smith can deploy in any other form of her life – any belief that she already has every right to broadcast online, or in her church, or in writing, or by holding a sign up in the street – is also an opinion she is entitled to enforce through the conduct of her business.

If the 303 Creative case sounds familiar, that’s because it’s more or less a rerun. In 2018, the supreme court heard Masterpiece Cakeshop v Colorado Civil Rights Commission, another case by a business owner challenging the same state law, this time a baker who didn’t want to make a gay couple’s wedding cake. In that case, the court punted, ruling that lower tribunals had mishandled the case, but not making a decision on the merits about whether an individual businessperson’s opinions trumped civil rights law. But the court looked very different in 2018: that punting opinion was written by Anthony Kennedy, who retired soon thereafter and was replaced by his protege, the beer enthusiast Brett Kavanaugh. Since then the court has lurched even further to the right, and has shown a willingness to indulge even the most far-fetched claims of Christian religious litigants.

But it’s worth considering what the court did not do when it agreed to hear 303 Creative: it did not grant certiorari on Smith’s claim that her religious freedom was violated by the anti-discrimination law. This is unusual, for this court: since the Trump justices joined the court, turning it from what was already a quite conservative institution into a maximalist, revanchist one with a culture-war axe to grind, the court has expanded free-exercise-of-religion rights quite rapidly – at least, so long as those free-exercise rights are being exercised by conservative Christians.

The court has even specifically used the constitution’s free-exercise clause to imply an entitlement to discriminate against homosexuals: in last summer’s Fulton v Philadelphia, the justices ruled that municipal agencies handling the welfare of children in need were obliged to work with a religiously affiliated adoption agency, even though that agency discriminated against gay couples in violation of city civil rights law.

But in 303 Creative the court is only considering Smith’s wish to discriminate as a free speech issue. This opens a new avenue for challenges to civil rights law, and will provide an opportunity for rightwing lawyers to begin unraveling the laws regarding non-discrimination in public accommodations in the wake of the civil rights movement, like pulling on a loose thread to unravel a sweater.

Though Smith wants to discriminate only against gay couples, and other exemptions to civil rights law are likely to focus on allowing open bigotry against LGBTQ+ people to be expressed in commercial life, there is no limiting principle that means that only gay people will be targeted. After all, if a website designer is allowed to decline to make a gay wedding website, what stops her from making the same claim to refuse an interracial wedding, or an interfaith one? Is she allowed to decline to make sites for birth announcements of children born to gay couples, or via IVF?

I keep thinking of the sign that Smith wants to put at the top of her future business’s webpage, the one that says she won’t make websites for gay weddings. It’s essentially an advertisement of her belief in gay people’s inferiority, an effort to exclude them not just from her own goodwill, but from commercial life. How different is such a sign, really, from those that advertised whites-only lunch counters, or the signs that the late Justice Ruth Bader Ginsburg recalled seeing in the windows of shops when she went on family road trips as a child: “No dogs and no Jews”.

It has become vogue, in rightwing legal arguments against civil rights law, to speak of the “indignity” imposed on anti-gay business owners who are forced to comply with anti-discrimination law. It’s a shame that the court doesn’t seem poised to consider the indignity of facing discrimination itself.

• Moira Donegan is a Guardian US columnist