A couple of years ago my brother, who has autism, was confronted by an angry audience member at the theatre. Or rather, his care worker was. “You shouldn’t let him out if he can’t behave,” the man said. My brother’s carers insisted he had as much right to be there as the aggressive man did, and it was the latter who eventually left, to a round of applause from the rest of the audience. When my brother’s carer told me the anecdote, it made me smile. People are kind, I thought.

Unfortunately, things don’t always happen this way for people with autism-spectrum disorders (ASD). On Sunday night, for instance, Tamsin Parker was thrown out of the British Film Institute (BFI) cinema in London for laughing “too loudly” during The Good, the Bad and the Ugly while she protested “I have Asperger’s.” Other audience members had called the 25-year-old a “bitch” and “retarded”. Witnesses described themselves as “shaking with anger” and feeling “sick to my stomach” at the scene. It was Tamsin’s birthday, and she loves the film, which she has seen eight times.

“A couple of audience members were yelling, ‘Shut up, bitch!’ and ‘It’s not that funny!’” said Tamsin, an artist and animator. “The thing is, it was funny. It was Eli Wallach playing with parts of guns, clearly improvising. Wallach hated guns, and he had no use for them, so it seemed like he had no idea what he was doing … I was distraught that I wasn’t able to watch the film the whole way through. This was a film that was very personal to me, because I first saw the film during a rough time in my life and it made me feel better about myself.”

The BFI has since apologised to Tamsin, and has offered her a private screening. The manager on duty, one witness told me, was “visibly upset” and said that had she known Tamsin had Asperger’s, she would never have let that happen.

This sad incident should be an opportunity to learn, not hound someone out of their job. Clearly, much better training is needed here for staff. But Tamsin’s mother, Lydia, is rightly furious that she was humiliated in this way. “Even if she were not autistic, no one should be treated as she was. All audience members deserve respect,” she told me.

Autism inclusivity in cinema and theatres has come on in leaps and bounds since my brother, who is also 25, and Tamsin, were small. Relaxed performances are now widespread, not only at the Globe and the National Theatre but in cinemas and theatres up and down the country, and are great for those who get sensory overload and as a result need sound and vision to just be a little bit less intrusive.

But people with ASD should not feel limited to these, segregated from the rest of society. They have as much right to attend an ordinary performance as anybody else. I admit that I have felt on edge taking my brother to the cinema before. You steel yourself for people’s reactions. When we took him to see Shaun the Sheep, he announced loudly: “SHEEP, BAAAAAAA!” whenever Shaun came on screen. People were lovely, but it was mostly children and parents in the audience. Would you be so tolerant?

It was the attitude of the audience members who abused Tamsin that really shocked me. The lack of humanity and compassion: the anger, where there is really so little to be angry about. Much has been made of the “hostile environment” Theresa May has tried to create for immigrants, but one wonders whether it exists for disabled people too. This is not a case of me being dramatic: the UK was last year criticised by the UN for failing to uphold disabled people’s rights. It pointed to the high levels of poverty for disabled people and their families as a result of benefit cuts. An earlier report by the same committee condemned “systemic violations” of people with disabilities. People who are ill and disabled are being sent to work, and some of them are dying.

To what extent have some of these policies, and the media coverage around them, seeped into the national psyche? Reported hate crimes against disabled people are rising even faster where children are the victims, a BBC investigation found late last year, with children and their families verbally abused in the street. These acts do not occur in a vacuum.

There is so much innovation occurring in film and theatre when it comes to disability. Madhouse re:exit, a performance by five artists with learning disabilities from the Access All Areas theatre company, recently took spectators at Shoreditch Town Hall on a fantastical tour through the history of the institutionalisation of disabled people. It’s currently in Manchester. Our Country’s Good, at Theatre Royal Stratford East, has a mixed cast of 17 disabled and able-bodied actors telling the story of their journey to a penal colony in Australia.

Productions such as these do crucial work in shifting attitudes. But it is our government’s policies, not to mention our media coverage, in which we truly need a shift, or disabled people will continue to be abused for having the audacity to exist in public; or, as in Tamsin’s case, for simply wanting to watch her favourite film, with her friends, on her birthday.

• Rhiannon Lucy Cosslett is a Guardian columnist