My brother can’t vote in the general election. He’s 26. Legally, he can: a lack of mental capacity is not a legal impediment to voting. But practically, he cannot. He’s severely autistic and epileptic. He can’t talk much, and he can’t write much. It’d be a bit like the time the Department for Work and Pensions sent him a giro that he needed to sign and take to the Post Office. Oh how we laughed. Cried. Laughed. You do a lot of both when you love someone who isn’t well.

For so many families in this country, the laughing part is getting more and more difficult. As my colleague Frances Ryan has written, disabled people are living in a hostile environment. If the Tories win on Thursday, which I fear they will, things will only get worse.

Millions will put a cross in a box next to a Conservative candidate, and I still don’t know how to process that

I know what Boris Johnson thinks about people like my brother, when he cares to give them any thought at all. Six years ago, he made a speech in which he said: “It is surely relevant, to a conversation about equality, that as many of 16% of our species have an IQ below 85”, before arguing that “some measure of inequality is essential”.

I know what his colleagues think, too: Iain Duncan Smith has essentially admitted that disabled people are easier to exploit, saying that “they often work longer hours and they forgo quite a lot of holiday because they love the whole idea of being in work”.

During this past week, the Conservative Hastings and Rye candidate, Sally Ann Hart, told voters that disabled people and those with learning disabilities should be paid less because some “don’t understand money”. In their ruthless worldview, disabled people are a minority who can be thrown under the bus.

Every time I hear comments such as these, I think: that’s my little brother you are talking about. A person I have loved, fiercely and protectively, for his entire life. The kid I swung around the room in his Spider-Man pyjamas, who would clamber into bed with me in the early hours for a cuddle, who, when you ask him who his best friend is, says my name, because when we were little I taught him how to do that because I didn’t want him to feel like he didn’t have one. My brother, who lives in a care home now, and whose care package is dependent on whichever government is in power.

The vast majority of us have loved someone so much that we would do anything to take their pain away – surely this feeling can somehow be translated into empathy for the most vulnerable people in our society? Yet on Thursday millions of people will put a cross in a box next to a Conservative candidate, and I still don’t know how to process that.

The Conservatives’ treatment of those with disabilities is ideological. For 10 years now, disabled people have faced cuts so brutal that they have been dying. More than half of disabled people don’t have enough care to meet their needs. Services have been cut to the bone, leaving people isolated and impoverished.

If you read the Guardian, the chances are that you know this. Elsewhere, there has been silence. I wanted to be a writer because people like my brother are voiceless, but I didn’t realise quite how voiceless they were until the past decade. The excoriating UN report accusing the government of inflicting “great misery” on the population of the UK through austerity – which disproportionately affects women, children and disabled people, infringing their human rights – came out a year ago. How much did it cut through? Are people voting Conservative because they don’t know, or because they don’t care?

My brother is just one person in this country who is reliant on the health and social care system functioning properly. Millions are in the same boat. And though some will need it more than others, that system is for all of us. If the social care system collapses, the ill, disabled and older people who rely on it will suffer, and so will the women who will be expected to plug the gaps and give up their jobs to care for their loved ones. So will all the overworked doctors, nurses and care staff – many from outside the UK – who have chosen to devote their lives to helping, treating and looking after people like my brother.

I firmly believe that we are standing at a fork in the road and that if we take the wrong path, we will lose a health and social care system that is so very precious to us. If you think that sounds dramatic, speak to some of the people who have already had that safety net removed and ask yourself if anything is worth that. Ask yourself if that’s the sort of place we want to be.

I’m voting Labour on Thursday, for my brother, and for all the other vulnerable people in our society who desperately need a Labour government. Labour, which has never been perfect, but which strives to protect those who feel powerless, and which respects their humanity. I know in my heart that a Labour politician will look at my brother and see him. They’ll see a young man with a big smile, big blue eyes and a personality. A young man who is worthy of care, and love, and protection. A young man who is so much more than a number on an IQ test, a drain on the system, a scrounger, someone to whom you can get away with paying a low wage. So much more than, as Johnson has it, the cornflakes at the bottom of the pile.

• Rhiannon Lucy Cosslett is a Guardian columnist