Maya Forstater doesn’t believe that people can change sex. For her, men are born male and women born female and that’s that; people can identify as another gender but can’t change their biological sex, no matter what surgery they have. She will use someone’s preferred pronouns out of politeness, but doesn’t feel bound to, because she fundamentally doesn’t accept that a man can properly become a woman. To some, that makes her a heroine, defending the sex-based rights that feminists fought to secure and doing so at great personal cost (she believes it cost her work as a tax researcher). But to others, it makes her a villain, denying the legitimacy of trans people’s existence.

Last week, Forstater lost an employment tribunal case, which, had she won it, would have allowed her to take legal action against a global development thinktank that did not renew her contract after she started posting views some staff found offensive on Twitter. A furore on social media followed, with JK Rowling tweeting that people could call themselves whatever they liked and live their lives in peace but “force women out of their jobs for stating that sex is real? #IStandWithMaya”. Lost in the ensuing hurricane, however, is what exactly standing with Forstater means.

Let’s start with what this case did not settle. The judge had nothing much to say about the way that biology – the raw and bloody business of being able to menstruate, or to be literally left carrying the baby, or to go through menopause, or to realise that the man following you home on a dark night is physically stronger than you – has been used against women for millennia. His ruling doesn’t change the political row that originally got Forstater tweeting, which was over whether adults should be allowed to self-identify as trans rather than undergo the demanding legal and medical process of getting a gender recognition certificate or GRC (which allows a trans woman to be treated for legal purposes as a woman). It doesn’t even tell us whether the thinktank was right or wrong to drop her, since the case never got that far.

This ruling was purely about whether Forstater’s views count as a so-called protected belief, like religious faith, which employers can’t discriminate against someone for holding. And while she met four of five legal tests for that, the sticking point was her insistence that a trans woman is still a man even if she holds a GRC confirming her legal status as a woman.

That’s what Forstater thinks. It might be what a number of other people think. But it’s not what the law says and the judge ruled that Forstater’s desire to be able to refer to someone by the sex she felt appropriate, even if that created an “intimidating, hostile, degrading, humiliating or offensive environment”, failed the fifth test – that a protected belief can’t violate human dignity or conflict with fundamental rights. Put simply, those seeking the protection of the law can’t ignore the protection it affords others. Even the vulnerable must acknowledge that others can be vulnerable too.

Crucially, that doesn’t mean women can now be sacked just for criticising self-identification or for objecting to trans women having automatic access to women’s prisons and domestic violence shelters. But what it means is objections shouldn’t be based on arguing that trans women are men really. The ruling explicitly says that it is “quite possible to accept that trans women are women but still argue that there are certain circumstances in which it would be justified to exclude certain trans women”, for example, from services used by rape victims or potentially traumatised women, just as the law currently allows. The central idea is that being a woman, trans or not, isn’t a licence to ride roughshod over the needs of others; that it comes with rights, but not infinite ones.

That cuts both ways, obviously. Forstater’s allies are justified in worrying that debate is being chilled by a small minority of trans activists resorting to aggressive threats online and physical intimidation of gender-critical feminists in real life. But if we are ever to achieve the “normal, open and democratic” conversation about sex and gender that Forstater says she wants, then it has to be conducted with mutual respect. This ruling offers a place, however difficult, from which to start.

•Gaby Hinsliff is a columnist for the Guardian and Observer