Disclosure: I am transgender. I first encountered this book in my late teens, and attempted to read it (prior to coming out/transitioning) to un-trans myself, or at least, to help contextualize why I felt the way I did. Even then, it was a bit much for me. I later picked it back up out of morbid curiosity.
Jeffreys book is an attempt to build off of the work of Janice Raymond's "The Transsexual Empire," the original trans-exclusionary radical feminist manifesto. As much as I hate to say it, Raymond's work had some merits in terms of its critique of the medical industry's enforcement of the gender/sex binary, even if the parts directly related to trans people were riddled with conspiracistic nonsense (ie describing trans women as "eunuchs guarding the harem," that is, suggesting they are agents of patriarchy attempting to infiltrate women's spaces to undermine their liberation). Jeffreys doesn't reveal her conspiracism in quite so explicit terms, but its foundations are certainly there. And, unfortunately, "Gender Hurts" doesn't offer anything particularly new or interesting to the critique of the medical industry that Raymond offers. It is also based on faulty reasoning, the arguments clearly being post-hoc rationalization for why she believes trans women are men, which I will explain below.
The argument can be boiled down to this: people are unable to change their sex, and are affected by sex-based socialization from birth that will determine the way they perceive themselves and others in a gendered world. Thus, because this socialization is inescapable, trans people will always retain characteristics of their assigned sex at birth (ASAB). Moreover, women's oppression is based on sex characteristics, and trans women do not have the characteristics on which this is based (vulva, uterus, etc) and thus do not experience oppression. For this reason, trans women cannot understand women's struggles, and have no place in the feminist movement, particularly in terms of women's separatism, which Jeffreys believes is the cornerstone of feminist activism, with the third-wave being a deviation from 'true' feminism. Gender, she argues, is the system which keeps women subjugated, and is, in essence, a collection of sex-based stereotypes. Gender should be abolished and "opted out of," with people identified solely by their sex.
There is a lot going on here. Firstly, two competing ideas: that socialization is permanent and sex-based stereotypes must be abolished. For the former argument, she gives examples of trans women who act masculinely as proof, in one instance saying that acting aggressively doesn't help a trans woman be seen as a woman. A supreme bit of sexism that is! She may have well said, "Don't you know women are meek and passive?" I doubt Jeffreys would openly admit to believing this as a nominal feminist, but the implication is very clear. And yet, elsewhere in the book, she argues that trans women reinforce stereotypes about femininity. So which is it? Are trans women bad because they are too masculine, or too feminine? The idea isn't consistent because, again, everything a trans woman does is proof of her innate maleness because Jeffreys already decided they were male before formulating any arguments. So for trans women, it's damned if you do, damned if you don't: they are expected to walk some invisible line between masculine and feminine to prove their womanhood, but that balance is both unknowable and unachievable. If you are going to maintain that *any* trans woman is a man, regardless of their presentation or behavior, then don't try to make presentation- or behavior-based arguments.
Similarly, trans men are branded with stereotypes based on their ASAB: they are painted as victims of the forces of a patriarchal and lesbophobic society, not responsible for their own decisions, and denied their autonomy. They are also noted to be "mostly lesbians," and if I recall correctly, male-attracted trans men are never addressed, presumably because it would make her argument equating transition to conversion therapy moot. While trans mens' motivations are centered in their presumed sexuality, trans women's is centered in sexual fetishism, because males are obsessed with sex, of course. I don't know how Jeffreys can claim to want to abolish sex stereotypes when she so vehemently and openly pins them onto trans people regardless of their actual actions, and implies they are innate and inescapable.
More on trans womens' sexual fetishism: Jeffreys adopts Ray Blanchard's "autogynephilia" theory to explain trans women's (and especially lesbian, bi, and ace TW) motivations to transition. This has the curious effect of making Jeffreys see sex where there is none, going so far as to take an excerpt of Julia Serrano's "Whipping Girl," in which she describes being a child and wanting to wear a curtain as a dress, and suggests this is an example of classic autogynephilia. There is absolutely nothing sexual implied in either the excerpt Jeffreys provided or the original story: it is only the story of a prepubescent child wanting to wear a dress. Jeffreys also suggests that trans women who deny sexual motivations to transition are simply lying, and adds that Virginia Prince, probably denied sexual fetishism to make her behavior more appealing to the general public. "They're just lying" isn't falsifiable and is entirely faith-based, and is just another example of the conspiracism that pervades the whole book.
And then the feminist aspect. She claims TW will never have the experiences of cis women, such as female genital mutilation, infant femicide/selective abortion, etc.. Interesting, considering Jeffreys is a white Brit, and probably also has no personal experience with many of the sex-specific issues she mentions. The "female experience" is presumed universal, and yet it is never defined: presumably because she knows giving a definition will inevitably exclude women who she would consider "real women." This universalization of women's experiences was a major criticism of second-wave feminism, which seems to have been dismissed by Jeffreys, as she continues to laud the second-wave in all of its worst forms. Using issues faced by some women in the third-world to attack trans women is as close to addressing WOC and women in non-western countries as Jeffreys gets. Otherwise, discussion of race is very conspicuously absent.
She misses the fundamental point: yes, gender probably did develop as a way of differentiating the sexes and keeping them in their reproductive and social roles. Which is why many transgender people are also gender abolitionists, myself included. But she holds that the sex binary is entirely justified and essential, defining women based on their reproductive role in the exact same manner as patriarchy. Jeffreys' politics are a reaction to the patriarchy, not a genuine deconstruction of it. Ironically, her glorification of lesbian separatism places patriarchy at the very center of her feminism: defined not by women, but rather by the absence of men. It is not surprising, then, that she has said elsewhere that being a lesbian simply means not having sex with men. Not even lesbians can be defined by their connection to womanhood: even that is centered on men.
There is a quote in the acknowledgements that stuck with me more than anything else in the book:
"I intend this book as a contribution to the considerable struggle that is presently taking place between mainly male transgender activists and radical feminists over who has the right to define what a woman is: women, or men who fantasise about being women."
And I am so mad that I wasted so much time reading this godforsaken book when I could've stopped right there. Jeffreys already decided that trans women were men, she assumes that the reader has already decided it, and if they hadn't, then that idea is solidified in them from the very start by begging the question. It is all backed up by arguments that are seemingly "common sense" when you have already made up your mind. It is all further drilled down by Jeffreys' highly emotionally-charged writing, whether it be in her gross descriptions of surgery (yes, surgery is bloody and gory. Thank you for your amazing insight), or the waxing poetic about how her free speech is being suppressed and she and her ideological contemporaries are martyrs, victims of the nefarious trans movement.