The LGBT campaign group Stonewall had harsh words for the annual Pride march through London, which took place on 7 July. The parade, said Stonewall, was too white; it would not be attending this year. The criticisms, which Pride described as “inaccurate” and “disrespectful”, won praise for Stonewall, which has been credited with taking a more radical direction under the leadership of Ruth Hunt. Meanwhile, Pride has also been criticised for being more about corporate “rainbow-washing” than sexual freedom: floats sponsored by high street banks dispense branded face paints, straight couples having a look-see outnumber the leather daddies, and you can’t even march without a wristband.

So when a small group of lesbians disrupted this year’s Pride, perhaps you’d imagine that Stonewall would be on their side. These women, too, think that Pride has grown stale and conservative. Like Stonewall, they accuse the march of letting down certain members of the LGBT coalition – specifically, lesbians. But instead of backing the protesters, Stonewall offered condemnation, saying they had put “people in danger” and “have no place at Pride”. In the calculation of my-enemy’s-enemy, Stonewall had decided that these women were the greater evil.

To understand this reversal, you need to understand why these women were protesting in the first place, and how their message slams headlong into the most intractable divide in today’s LGBT movement. The group, which calls itself Get the L Out, carried banners proclaiming “lesbian not queer”, “lesbian = female homosexual” and “transactivism erases lesbians”. For Stonewall, which has made trans inclusion a central part of its renewed mission since Hunt took over in 2014, this was beyond the pale. Stonewall’s position can be summed up in one of its popular T-shirt slogans: “Some people are trans. Get over it.” Get the L Out was resolutely failing to get over it.

It wasn’t just Stonewall that condemned the protesters. Pink News and the Guardian called them “anti-trans”. On Twitter, the protesters were called “terfs” – trans exclusionary radical feminists – an epithet that is frequently accompanied by violent threats and dehumanising rhetoric. Pride apologised for their presence. If the mark of successful direct action is getting your message out, Get the L Out failed. Never mind assessing if their grievance was legitimate – most of the coverage failed even to describe what it was.

Yet criticising the brand of trans activism prominent on social media and in university feminist societies was always going to be unpopular. When discussing modern gender politics, anything more complex than the “get over it” line leads to charges of bigotry, violence and even – at the most hyperbolic end – genocide. (Not recognising someone’s innate gender identity is the same as denying their humanity, and could lead to suicide, runs the reasoning.)

For some lesbians, clearly there’s enough at stake to persist in the face of those accusations. The logic of trans activism – not the universally held opinions of all trans people, but the kind of political positions espoused by Stonewall – demands the redefinition of same-sex attraction to same-gender attraction. And for lesbians, that has disturbing implications.

If “trans women are women, full stop” – even if they retain male genitals, as most do – then what it means to be a lesbian changes dramatically. A lesbian who refuses to consider a trans woman as a sexual partner is guilty of denying that trans woman’s gender identity. Online, such women are derided as “vagina fetishists” and transphobes.

Why does this matter so much? Because lesbians have consistently faced everything from mockery to violence for insisting on boundaries to their sexuality. For lesbians who know the history of “corrective rape” as a weapon against gender non-conforming women – the practical application of the old saw that all lesbians need to “fix” them is a dose of penis – this is a deeply alarming development in LGBT politics.

This isn’t a frivolous concern. In 2012, Planned Parenthood ran a conference called “Pleasure and Possibilities” which included a workshop on “Overcoming the Cotton Ceiling: Breaking Down Sexual Barriers for Queer Trans Women”. The title referenced the feminist concept of the glass ceiling – that is, the invisible barriers to promotion at work. Cotton meant underwear. Getting inside women’s knickers was treated as a discrimination issue equivalent to failing to become a CEO.

Unsurprisingly, gay men haven’t faced the same pressure to be “inclusive” on pain of being called a bigot. Trans men showing up on your dating apps is annoying when you’ve got no interest in vaginas, but ultimately ignorable. Meanwhile, sites such as Autostraddle or Vice’s Broadly publish guides on how to have “lesbian sex” involving male genitals. I’ve yet to see gay men instructed on how to manipulate a clitoris.

Misogyny doesn’t vanish at the flicker of a rainbow. When women aren’t addressed directly and specifically, women get ignored; and when lesbian, gay, bi and trans are gathered under one label, lesbians lose. Lesbians are even losing themselves as a group, as it becomes impossible to organise woman-only events without foundering on the controversy of how to define “woman”. Butch lesbians like the comedian Hannah Gadsby are asked when they’re going to “come out” as trans men, as Gadsby relates in her Netflix special Nanette. If you don’t look feminine, some gender identity schools of thought say you must be a male in your deepest self.

Where biological sex meets sexual attraction, there is an unavoidable conflict. Where there’s sexism too, that conflict’s casualties will be female. Not every lesbian is ready to get over it.