A dead fat person is being cut up and broadcast on the internet as you read this. It is happening, apparently, as an exercise in public health education and not for the shock value of watching a mortician hold up an anonymous woman's liver and describe its moral failings in the manner of an ancient Egyptian death god reduced to fodder for BBC Three.

The programme is billed as sensitive, and all about letting people know how dangerous it is to be fat, and not at all like a fairground freakshow. That’s why it's called Obesity: The Post Mortem and why it's being promoted with stills of the corpse, generously donated by an American woman who consented for her remains to be used for the purpose of medical science, although this show pushes the definition of public good into the grisly arena of entertainment.

I imagine that a great many people tuning in to Obesity: The Post Mortem will not be fat. What message will they be receiving? Fat people are not like you. They are less than human. They have sinned against their own flesh and deserve to have their corpses violated. They brought it on themselves. They deserve your pity, your smug superiority. They deserve to carry the full weight of your subsumed anxieties about greed, consumption and control, so you don’t have to. It’s for their own good, isn’t it?

This month, it was reported that in a desperate hunt for savings, the NHS will start refusing overweight people basic operations. There was almost no outcry, beyond those sections of the internet where overweight people with the temerity to think of themselves as human beings with the same right to healthcare as anyone else congregate with as much courage as they can muster while being deemed acceptable targets for the popular opprobrium sloshing around society like excess bile.

Fatphobia is acceptable discrimination at a time when prejudice itself is fast becoming more acceptable as a mode of human interaction. The justification for abusing and dehumanising fat people, when justification is sought at all, is that “fat is unhealthy”. I am not here to discuss whether or not fat is unhealthy — although it bears repeating that being overweight is not an absolute predictor of ill-health in the way that, for example, smoking is. I am not interested in being shown studies and scare stories, because — guess what? I've already seen them. I already know. Barely a day goes by without some reminder that fatness is a source of disgust, and I'm not overweight. My friends and loved ones who are cannot avoid being reminded about it every time they cross the street or open a browser window.

But let's shove aside the ongoing, active debate about the actual correlation between size and health and assume for a moment that it’s all true, that fatness is both as clear a predictor of sickness as we're told and entirely within the control of the individual, whatever their class, resources and physical limitations. Why would that be any reason for abuse, ritualised shaming, and denial of medical care?

Most of us know that booze is bad for you. And yet I struggle to imagine a public service broadcaster greenlighting a show called Alcoholic Post Mortem. Most of us also know that smoking is a really dreadful life decision. And yet people with lung cancer and emphysema are not refused medical care, treated as morally suspect by judges and employers, or screamed at in the street. Fat people, and particularly fat women, face discrimination at work, at school, in the courts, and even from healthcare professionals, many of whom refuse to treat other illnesses unless the fat itself is dealt with. Fat women are less likely to be promoted and paid what they’re worth. Fat women are taught that they are unworthy of love, care or respect. In 2016, fat is still a feminist issue.

However hard it is to be a fat man, it is much harder to be a fat woman. Or, indeed, any woman deemed larger than she should be — you do not have to be considered medically overweight to face a measure of the discrimination sexist society hurls at any female person who dares take up more space than she's told. Men are expected to take up space in the world. Men can be rich, successful and physically large. Men, most importantly, are not expected to conform to socially determined ideals of attractiveness in order to be considered human.

Our culture is full of actors, comedians, artists and politicians whose weight would be the best-known fact about them, a fact they would be expected to answer for every moment of every day, if they happened to be women. There is a particularly poisonous strain of fatphobic sexism growing on the alt-right that interprets the sheer existence of fat women as a personal insult to men everywhere. It is also about class. Fat, increasingly, is seen as one of the “bad decisions” we associate with poverty, particularly female poverty - and it's true that many people on low incomes, people working exhausting jobs for little pay, are less able to afford the time, money and attention it takes to be acceptably slender by modern standards. Fat-shaming is a way of policing not just female bodies, but working-class bodies, and if you're both, well, you probably deserve having your heart cut out and held up on television to be gawped at.

As a proud feminist who writes a great deal about bodies and social control, I have been slow to speak out on this, for several reasons, not all of which I'm proud of. I was shy to raise my voice against fatphobia, because I am not fat myself, and never have been, although that doesn't stop misogynist keyboard-jockeys from calling me fat every single day, because “fat” is shorthand for “a woman we don't like, who takes up more space than she deserves.” I'm writing this because several fat activists have called for allies, and I thank them — particularly activist and artist Kiva Bay — for their time and patience.

I've been shy to speak up for the same reason that many of us are shy to speak up. I’m afraid of fat. I've spent a lifetime internalising the message that fat is evidence of personal failure. I spent years in eating disorder hell, starving away any hint of softness on my body, because however awful it felt to be weak and hungry, it was surely worse to be fat. Fat, particularly female fat, represented for me what it represents for so many of us — weakness, unabashed desire, the cardinal sin of non-conformity to the narrowing ideal of beauty that is part of the pageantry of female coercion in this society.

There's a feeling that if we were to admit that fat people have as much right to dignity, respect and decent treatment as anyone else, fatness itself would somehow run rampant, infecting anyone who dared offer it moral space. It’s a type of magical thinking: by continuing to abuse and dehumanise fat people - or to stand by while the abuse continues - the rest of us protect ourselves from fat, and if a few million lives are quietly made miserable in the process, that’s a small price to pay. Think of the children.

A great deal of bigotry is rationalised in the name of hurting people for their own good. It has never been proven, however, that shame and abuse is an effective way of treating any health condition. If you actually want people to change their behavior, the easiest way to do that is to start treating them with respect. But that's not the best reason to do it. Fat people deserve basic respect, solidarity and support in the face of harassment, not because it will get them to lose weight, but because they are human fucking beings who deserve human fucking dignity, whatever their size and shape. Fat people have been saying this for years. It's time for not-currently-fat people to say it with them. I've spent too long not speaking up, thinking that not actively participating in the bullying was enough. It wasn't. I promise to do more to oppose fatphobia — starting today.