When I was in the depths of postnatal depression, I searched social media hungrily for some sign that my experience of new motherhood was not abnormal. No such luck. Even confirmed feminists I knew were going along to Mummy and Me or Stay and Play, singing nursery rhymes in big circles, and then making self-deprecating jokes about it on Facebook. “I know all the words to Incy Wincy Spider now.” Embarrassed emoji.

I went along, too. But after baby groups I felt degraded, as though my hard-earned identity as a valuable, thinking person and a mature human being was being crushed. I was a grown woman, with a degree and a mortgage, and yet I was made to sing “Say hello to the sun”, and mimic the shape of a cloud with my hands. One day, when I laid my son down under the baby gym during the break to write a text, the administrator came over. “You know,” she said, “when mine was this age, I didn’t want to look away for even a moment. It’s so important, this time with him. You’ll never get it back.”

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Had anyone said that to my husband, I wondered? I felt like I was being annihilated. And this came on top of the trauma of the early weeks. I had barely recovered from childbirth before a painful experience of breastfeeding and the relentless agony of sleep-deprivation. Add to that the abrupt depletion in the first three or four days after birth of the happy hormone – oestrogen – that was surging through my body during pregnancy.

To me, anger is a reasonable reaction to all this. But I couldn’t own my anger, because I was being crushed by fantasy. I had to be happy. The cult of motherhood was being imposed at every turn, a life-destroying expectation of maternal perfection. So I repressed my rage, my anxiety, my stress. I smiled at the baby, because what kind of mother shows anger to a newborn? Inside, I was suffocating, and textured into my anger came something terrible: maternal guilt.

What happens when anger and guilt are repressed? They implode, unpredictably and unexpectedly. For many women, myself included, this is how postnatal depression (PND) starts, as repressed trauma and sustained stress, exacerbated by guilt and shame, jolt to the surface and pull you into a dark hole.

I am still fighting the guilt and the depression. I am winning, but the black dog is never far from my heel. Now, at six months old, my baby goes to a childminder four days a week, where he is cherished by infant-school children and a retired teaching assistant who does Ofsted-regulated baby sensory, rhyme time and tummy time with him. His life is rich and full, happy and safe. And he is much less likely to become a one-year-old who is scared of strangers and can’t leave mummy’s side. Better for me, better for him.

But the cult of motherhood is ubiquitous. I deleted my baby apps when I realised they only mentioned dads as a subsection, like a type of buggy. The vast bulk assume mum-exclusive care. The breastfeeding establishment, too, takes no prisoners: six months exclusively, says the NHS; two years ideally, says the WHO; don’t do mixed feeding EVER, I was told by my National Childbirth Trust counsellor. Any woman who doesn’t want to stay at home and nurse for at least six months is thrown under the bus of shame.

But it’s also the story we tell each other, the fantasy we inflict on women when we say things like: “There’s nothing more fulfilling than being a mum.” On social media, we gloat and swoon. You have to get women on their own to hear the truth. Privately, new mothers say things like, “I’ve never been so tired. Nobody told me this would be so hard. I feel like I’m doing everything wrong. When I breastfeed, I feel like a cow.”

What made us think it’s a good idea to put women in this situation? I have a strong, deep bond with my son, but I knew at six weeks that I didn’t want to look after him all day, every day, alone. Rationally, this is a reasonable decision. But making this decision, and telling people about it, felt like announcing I was handing him over to a cult.

Subtle and not-so-subtle indoctrination, from the toy ovens and baby dolls of nursery school to my breast-idolising NCT classes, has inculcated a sense that glowing motherhood – a motherhood in which you give 100% of your time, all of your self, and none of your rage – is natural and right, and that anything different is deviant, unworthy, unwomanly.

Whereas the truth is, there is nothing less natural than leaving a woman alone with a baby, day in, day out. The American chef Aarti Sequeira, who has campaigned for women with postnatal depression, called her mother in India when she was in the depths of her own postnatal illness. Her mother replied, “I don’t understand how they’re doing it in America, because if you were here in India, for the first month you wouldn’t do anything”. In many parts of the global south, communal and extended-family parenting, including shared breastfeeding remain commonplace. Humans evolved to care for babies as a tribe. Continuous mothering by the birth mother was a last resort for primates. Socially isolated mothers are far more prone to PND. Without a protective group, neural threat systems kick in and we feel mortally threatened. In short, the exclusive mother-baby cult is a bizarre modern western fantasy that neglects the social, physical and psychological needs of women.

Women must be allowed to have children and to resume social, balanced lives as soon as they like, without guilt or shame

As the saying goes, it takes a community to raise a child. Shared parental leave is an important step, but aside from the fact that men don’t seem to opt for it unless they’re forced to (and I’m not against making paternity leave compulsory), it’s not actually the answer. I’m not surprised men are reluctant. The problem is that women don’t have the resources – practically, philosophically or emotionally – to also refuse.

The answer is genuinely socialised childcare – workplace crèches, free nursery care from zero months, not three years – and a radical reconstruction of our perception of what babies need and what women deserve. The kind of social cohesion in child-rearing promoted in Denmark is cited as a reason Danes are among the happiest people in the world. We need a society that values women enough to allow them to both have children and to resume social, balanced and nurtured lives as soon as they want to, without guilt and shame. Not for women to choke off their own emotions and ambitions in order to feed a domestic fantasy made up by advertisers in the 1950s.

• Cerys Howell is a writer and PhD student