I’ve been fat my whole life and in the early 2000s, I discovered fat activism. It opened my eyes to just how badly fat people are mistreated and subjected to widespread discrimination: in education, employment, and healthcare, just for starters. But many people of my liberal and progressive ilk simply haven’t caught on: the kindness we preach doesn’t seem to extend to people who live in larger bodies.

It’s not just my impression: hard data backs up how entrenched fatphobia remains in society. When it comes to race, skin tone, disability, age and sexuality, both conscious and unconscious bias against marginalised characteristics appears to be on the wane, according to research undertaken at the Harvard department of psychology. There is one notable exception: body size, which was the only form of unconscious bias that is actually increasing. And conscious bias towards larger people was found to be decreasing the most slowly of any of the categories investigated.

I often faced fatphobia as a child, being bullied, teased and excluded for my size. I remember being seated in a circle of kids, eating our lunches in a grassy playground, when a prepubescent boy pointed at each of us in turn: “skinny”, “medium” or “fat”, he casually pronounced us. I was the only girl pronounced fat, and I was mercilessly teased on that basis. These days, such taunting is still all but guaranteed when I write about such subjects in a public forum. And even academics who learn I am working on the topic of fatphobia are often quick to change the subject, turning away in embarrassed silence.

So why are we getting better on most forms of bias while becoming arguably even more fatphobic as a society? Part of the answer has to do with the fact that fatness, unlike many other forms of marginalisation, is perceived as a choice. But careful attention to the evidence on this topic paints a different picture. Numerous factors – from our inequitable food environment to economic injustice to stress to trauma to common health conditions and medications – dictate our size, and a combination of these have contributed to an uptick in fatness in both the US and the UK, among other countries, in recent decades.

The moral panic over a supposed explosion of fatness is not just stigmatising: it often overlooks the changing classification standards for fat bodies. Our genes play a huge role in determining body size, too, with genetic factors accounting for more than 70% of the variance in body size across the population. To put this in perspective, this makes weight just a little less heritable than height, which is about 80% heritable.

What these factors all have in common is that they are, by and large, unchosen. True, many people can lose a modest amount through diet and exercise in the short term. But virtually every long-term diet study to date shows that the weight comes back for the vast majority of people. Many, if not most people, end up heavier than when they started.

Wherever you come down on the question of the health risks of fatness – which I would argue are exaggerated – there is simply no excuse for rampant discrimination. In the health care sector, this is particularly widespread, with doctors even openly admitting that fat patients are more likely to annoy them, that they view us as a waste of their time, and have less desire to help us. Don’t fat people deserve acceptance, compassion, and crucially, adequate healthcare?

As fat people, we’re often made to feel ashamed of ourselves and hence try desperately to make ourselves smaller. (And believe me, I understand; I have been there many times myself.) We often don’t want to identify as fat, let alone to stand in solidarity with still larger people, says the fat activist Aubrey Gordon. Those in smaller bodies may desperately cling to the benefits of “thin privilege” and, for many, fatness is a spectre, a nightmare, a cautionary tale. Instead of joining political forces to demand better treatment, we work on ourselves, to shrink ourselves, and avert our eyes from larger bodies.

But this is not only a sad waste of energy for the many of us who are likely to end up fat in spite of this, as we grow and age and sag; it is also a betrayal of people who deserve so much better. This includes, of course, our children, with fatness being among the most common bases for childhood bullying. Far too many children fall prey to disordered eating (which affects one in five worldwide) or even full-blown eating disorders, with being deemed overweight by parents being one of the biggest risk factors.

It shouldn’t be remotely controversial to say that, no matter the size of your body, you deserve what many fat people are currently denied: fair educational and employment opportunities, good healthcare, and access to private and public spaces, just like anyone else. The fact that this actually needs to be said is a depressing reflection of how willing we are to throw each other under the bus in our attempts to get aboard it. True political progress requires that we pause and look around and extend a sympathetic – better, solidaristic – arm to everyone. There should be no limit to our capacity as humans for inclusivity; there should be no size restrictions either.

• Kate Manne is an associate professor at the Sage School of Philosophy at Cornell University. Her books include Entitled: How Male Privilege Hurts Women and Unshrinking

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