The writer claimed to be "the ultimate outsider", a 35-year-old lesbian who had lived as an Arab Muslim in the United States, and was now living as a Sunni Muslim in Syria. On her blog, A Gay Girl in Damascus, Amina Abdallah Araf al Omari described her romantic relationships, involvement in street protests, and her father's ferocious response when the security services came to call for her. The site's audience built quickly after its February launch, and when it was reported that Amina had been abducted from a Damascus street by armed men, campaigns for her release began immediately.

So it came as a surprise to find that Amina was in fact a white, heterosexual married man called Tom MacMaster, who comes from the US and now lives in Edinburgh. Admitting the hoax on Sunday, MacMaster was initially bullish, writing that he didn't believe he had "harmed anyone – I feel that I have created an important voice for issues that I feel strongly about". But by the next day, with LGBT campaigners in the Middle East and beyond expressing disgust and some saying they could have taken significant risks in asking questions about Amina's safety, he was considerably more apologetic. He wrote at length about his reasons for creating Amina (he enjoyed writing; he was "trying to enlighten people") and apologised to a number of people by name. These included the woman whose online photos he had stolen to depict Amina, the woman he had apparently been having a deeply involved online relationship with, and someone called Paula Brooks, who set up a website called LezGetReal ("A Gay Girl's View on the World") in 2008, giving "Amina" an early platform.

Then the story took another twist. Paula Brooks wasn't what she seemed either. In fact, the woman who was purportedly both lesbian and deaf – explaining why she couldn't talk to reporters on the phone – was actually a retired US Air Force pilot from Ohio called Bill Graber. He told the Washington Post that he had set up his site with "the best of intentions", and had used it to argue against the US military's Don't Ask Don't Tell policy. But this defence was greeted with anger and astonishment by many who had believed him. One commenter on LezGetReal wrote that he has "completely delegitimised us actual queer bloggers" and Louise Carolin, deputy editor of lesbian lifestyle magazine Diva, says she is furious about both hoaxes. "They remind me of the cancer blogs that have been revealed as hoaxes," she says, "some of which have been a deliberate financial fraud, and others just an emotional one. Many lesbian women feel very isolated – especially if they're from a minority ethnic or religious background where it's difficult for them to come out – and the internet is somewhere they go for support and a sense of community. [MacMaster's] blog tapped into a lot of very real experiences for people in Syria and the Middle East, and also people here who identified with it. I think it's absolutely indefensible."

So why did they do it? It's certainly not the first time that men have impersonated lesbians online. There have been ugly cases of men posing as lesbians to entice young women to send them naked pictures; women who run lesbian forums have written of their suspicions that men are infiltrating their sites; dating experts have warned lesbian clients that they can't know whether the people they are corresponding with online are women "or a male internet porn or sex addict, just looking for a thrill". Carolin says: "It's very, very common for men to set up log-ins for internet forums run by or for gay/bi women. The motivation is usually clearly sexual or malicious, so they're usually spotted very fast by other users and deleted by moderators."

In the case of MacMaster and Graber, sexual gratification doesn't seem to have been the prime motive, although there are certainly signs that the two men may have got some erotic thrill from pretending to be lesbians – "Amina" apparently often flirted with "Paula". But as Carolin says, "MacMaster and Graber are unusual in that they chose to operate with such a huge sense of entitlement at such a high level, not just for a brief kick but apparently under the delusion that they were doing something good for lesbians. And they weren't just infiltrating a website or forum run by lesbian or bi women, but actually running the operations themselves."

In fact, as the psychotherapist and feminist writer Susie Orbach says, they seem to have been using these lesbian personas as a "double inversion – exploiting the 'illegitimacy' of the person they were impersonating to give themselves legitimacy". In apologising, MacMaster wrote that he had seen "lots of incredibly ignorant and stupid positions repeated on the Middle East" online, and had found that when he, as "a person with a distinctly Anglo name, made comments on the Middle East, the facts I might present were ignored and I was accused of hating America, Jews etc. I wondered idly whether the same ideas presented by someone with a distinctly Arab and female identity would have the same reaction."

And so he took on the persona of someone whose views are so rarely heard or listened to. Ayla Ahmed, a Pakistani lesbian writer, sees this as a very distinct form of egotism. "I think the rise of identity politics – a concerted effort to give marginalised people a voice – has made some white heterosexual men a little paranoid or insecure," she says, "so they invent an oppression and position themselves as victims. I would assume MacMaster felt ostracised from his 'own people', as it were, and as a result took on a persona in which he felt he could be heard without criticism. This seems to me to be a hero complex that's really a very smug delusion – 'Look at me, look at how I'm standing up for oppressed people.'"

Both cases, says the feminist writer Beatrix Campbell, can be seen as a portrait of male dominance – men needing to infiltrate discussions where they wouldn't otherwise have an obvious, and certainly not an authoritative, place. She says that when it comes to MacMaster, "he clearly doesn't have a clue about what the politics of identity has tried to reveal, which is, first, that we are not all white men, and second, that white men are always treated as the supreme identity. Here he is, doing the same thing – claiming the virtue of representing a repressed condition, in a repressed part of the world, deciding that he is the person who will give that voice. That is the supreme irony. Here we have a boundaryless white American boy absolutely habituated to a kind of supremacy, and reiterating that supremacy through his blog. It speaks to an omnipotence that doesn't understand its own limits." As Carolin says, he is ignored the first rule of being an ally, which is "don't try to speak for the people you're trying to support".

While there are worries that this will undermine the lesbian blogosphere – creating a question mark over all who write about gay issues online – Campbell suspects it won't do too much lasting damage. "Internet life is full of hoaxes," she says, "it's full of virtuality. Lesbian bloggers who are embedded and authentic will continue, and all these others will fall away."

• This article was amended on 11 August 2015 to anonymise one of the people quoted.