• Warning – contains spoilers!

Three Billboards Outside of Ebbing, Missouri is nothing if not a divisive film: even as it is being heralded as an Oscar-heavyweight and an “uproarious delight”, it is being criticised for the way it pushes its audience’s sympathies towards a racist monster-cop who is never held to account for his brutalisation of black Americans.

But for me the film was uncomfortable for a different reason. As a 21-year-old woman with a form of dwarfism, what stood out was Three Billboards’ depiction of suicide and disability. The portrayals of both Peter Dinklage and Woody Harrelson’s characters subscribe to the reductive logic that personhood is only valid in the able-bodied.

Dinklage plays James, who introduces himself as the “town midget” and whose primary function in the film is as the butt of many jokes. In the cinema where I saw Three Billboards, the audience cackled whenever James spoke. This was painful enough as a response to the script’s cheap shots at short-person jokes – for example when James excuses himself to use the “little boys’ room” or is asked if he can juggle.

But I was more baffled when the people around me laughed at distinctly unfunny scenes of James playing pool, holding a ladder or asking Mildred (Frances McDormand, whose performance has put her in the running for a best actress Oscar) out to dinner. The source of this hilarity seemed to reside in the mere fact that James existed and that he was short; how funny that he, with his non-conforming body, should have the audacity to present as a desiring subject! What a laugh! This clunky reliance on ableist tropes as a form of humour was disappointing coming from a film lauded for its “moments of sharp, cinder black comedy”.

To its credit, the film uses this instinctive prejudice as a lure to criticise Mildred’s, and implicitly the audience’s, false sense of superiority. In his only significant scene, James goes out to dinner with a clearly embarrassed Mildred who feels she is forced to repay him for providing a false alibi. After a requisite number of height-related gags, Dinklage delivers a powerful monologue that flips the script on Mildred: “I know I’m a dwarf who sells used cars and has a drinking problem, I know that. But who the hell are you, man? You’re that billboard lady who never ever smiles, who never has a good word to say about anybody … and I’m the one who’s not the catch?!”

For a moment, James comes close to being humanised, and I can almost see why Dinklage praised Three Billboards as “one of the best scripts I’ve ever read”. But the effect is ruined as James storms out of the restaurant, the camera lingering on his tear-stained face as he delivers the plaintive closing line: “I didn’t have to come and hold your ladder.” As such, the transition from comic relief to object of pity never breaches the “us” and “them” divide, and James is doubly shunned for the sake of Mildred’s character development.

The other jarringly ableist storyline in Three Billboards is that of Woody Harrelson’s character, chief of police William Willoughby. Diagnosed with cancer, Willoughby takes his own life ostensibly to save his family and friends from the burden of his long, inexorable decline into illness. By doing so, he transcends the physical reality of his disease and becomes an almost godlike voice of authority in the film. His letters to Mildred and Officer Dixon are revered as emotional centrepieces of the narrative, and it is only when coming from beyond the grave that they truly take his advice.

This plot device is troubling in its reliance on preserving a characterisation of Willoughby as the hypermasculine, able-bodied leader of the town who actively ended his life, rather than a sick man who passively succumbs to his disease. His words doubtless have more import in the form of a suicide note than they would have coming from the mouth of an ailing cancer patient.

In her essay Illness as Metaphor, Susan Sontag argues that the physical reality of illness is worsened by the cultural tendency to view it as a metaphor – as a judgment or manifestation of a person’s inner character. Sontag herself was treated for cancer and observed the destructive inclination to view the disease beyond its physical reality and instead as a metaphorical “diminution of the self”. Three Billboards buys into this tendency by glorifying Willoughby’s suicide rather than letting him become ill with cancer; as long as the memory of him is untarnished by disease, he is afforded the dignity and authority reserved for the able-bodied.

Similarly, the film portrays James’ dwarfism as a metaphoric as well as physical disability. As a person with dwarfism, I am fine with the literal reality of my disability. Unlike some, I see the word “disabled” as an accurate descriptor: I am unable to reach tall shelves, unable to carry heavy things, unable to catch buses with stairs. But these inabilities do not exceed the corporeal: physical growth is not a metaphor for emotional growth. I am not, as this film seems to imply, unable to love and to be loved.

• In Australia, the crisis support service Lifeline is 13 11 14. In the UK, Samaritans can be contacted on 116 123. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. Other international suicide helplines can be found at www.befrienders.org