"It's a girl, but she's got Down's. Do you still want her?" I will never forget that conversation. It was the day we chose to have a child with Down's syndrome and the beginning of a journey that would lead us to decide not to have a child with Down's syndrome.

She was the most beautiful child you could imagine. People would literally stop me in the street to comment about her. She could light up a room with a single smile. Nobody who knew her would ever forget her.

She was also a challenging child. For months she was plugged into breathing apparatus at night that made her sound like Darth Vader as she slept. In addition to her extra chromosome she also had hypermobility which meant that walking was always going to be a challenge for her.

She was the most affectionate child. She had an emotional intelligence that far outstripped our other children at her age, and yet she never made demands. As a toddler she was quick to make friends and slow to lose them.

She was delayed in her speech. She needed additional resources to be able to do things that other children her age could do easily. We watched a lot of Mr Tumble. And she taught us the signs as much as we taught her.

We chose to have this little girl in our lives. We were her foster parents for the first three and a half years of her life. Sometimes caring for her earned us respect and sometimes it earned us pity. Sometimes our hearts burst with pride, and sometimes with frustration. Most of the time her syndrome made no difference – she was first and foremost a person in her own right. She came on every family vacation, she was at every meal, every birthday party, and in every family photograph. She was a full member of our family. But then she wasn't.

We chose for her not to be in our lives after that. Maybe we could have put ourselves forward as her adopters, but we didn't. Was it because we thought she would be better off with a family who could love her more than we ever could? Was it because we wanted to be available to look after other children? Was it because we couldn't cope with the long-term commitment of a child with disabilities? These impossible questions haunted those final months that she was with us and still do. It happens with every child we foster.

I know a little about what it is like to choose to be a parent of a child with Down's syndrome and also to make that heart-breaking decision not to be a parent of a child with Down's syndrome. And so the recent debate on whether we are one step closer to creating a world without the heartache and privilege that is Down's syndrome is for me personal, painful and poignant.

As I look at the debate I can see three very positive changes that are going on in our society.

First of all we are making astonishing steps forward in medical technology. As someone committed to encouraging scientific research we can celebrate advancement. We are able to perform medical interventions that could only have been dreamed of a generation before. These medical advances are already used to help children and adults with Down's Syndrome live healthier and longer lives. They are also being used to give potential parents advance information of whether or not their child has Down's syndrome. This is good.

Secondly we are making slow, but significant steps to becoming a more gender equal society. After generations where women suffered exploitation and subjugation, it is right that as a society we have recognised the autonomy of women over their bodies. This is good too.

Thirdly, the increasing celebration of diversity in our society has had huge positive effects. Even in the last decade there has been very positive moves to recognise that we should value people of all races, abilities, sexual identities and persuasions. In many ways we have become a more inclusive and welcoming society. We have built laws to protect people from hate crimes and discrimination, and made better provision for children with special needs in schools. Down's syndrome is much better profiled in the media and in the community, and as a nation we can be proud of our actors and athletes who have championed this. Once again this is good.

But what happens when these three positive developments collide? One plus one plus one does not equal extra chromosome 21. Three rights seem to me to make a wrong when it comes to the expectation that the new non-invasive early screening test for Down's syndrome will mean a massive increase in terminations and a massive decrease in the number of children with Down's syndrome born in the UK. Suddenly Down's has become positioned alongside a disease like polio to be eliminated as efficiently as possible, and the screening is seen as a cure, although to me it seems on par with the idea that we could cure racism by eliminating black people, or cure dementia by terminating old people. The new screening has caused a moral debate in a world that values diversity in others, but perhaps struggles to embrace that diversity when it comes to the sort of children we want.

In my job recruiting foster carers and adopters, I have noticed that many potential parents often start out looking for children that will suit them, fit into their lives, fulfil their dreams and ambitions. When the children in the care system don't match up to these profiles, this leads to an impasse. Children, especially those in sibling groups, from ethnic minority backgrounds, or with additional needs are left waiting for families.

My charity's message is that parenting is not about getting the children we want, but instead it is about the adults stepping up to be the family that the waiting children need. That means we ditch the pernicious, consumerist idea of selecting which children are worthy of love based on their genetics, ethnicity, gender or abilities and start showing all children the love and acceptance they deserve.

I want to change the way that our nation considers parenting. Contrary to some of the language used around the decision to terminate pregnancies with a diagnosis of Down's syndrome, there are no perfect children. In fact the majority of all children born will have at least one of the many thousands of genetic disorders. The majority of children will be a 'burden' on their families or their communities for at least a proportion of their lives. The majority of children will face educational, medical and/or behavioural challenges during their lifetimes. The majority of children will, sadly, face a degree of social exclusion or bullying during their childhoods. And an additional minority of children will have the added difficulties of early life trauma and displacement. To be encouraged to terminate a pregnancy because children may face these things seems to show a naivety around parenting. No one gets to choose a child that will not have to face any of these struggles. Being a parent is all about helping our children to navigate these difficult issues and the complexities of life in a modern world, as well as helping them to strive to reach their potential, and of course loving them whatever.

The little girl that was part of my family for three years now has a new family. That family began their journey to adoption because they specifically wanted to welcome and love a child with Down's syndrome. I have since met many, many families who have set out to grow their family with children that other people deem unwanted. These adopters give me hope. Conforming to cultural expectations is easy. Condemnation and criticism are easy. Committing to love a child unconditionally in this context could yet turn the tide of public opinion.

My hope is that we will see a whole new generation of people who will demonstrate through the way they open their lives and their homes to children in need that our world is a better place. My prayer is that we would forge a future where all children, whatever their difficulties or disabilities, are valued equally.

Can we rise to the (very rewarding) challenge of being the parents for a new generation of children with Down's syndrome? Can we show the world that they are not an unwanted community not just by shouting loudly in debate but by showing up to care for children with additional needs in our care system through fostering and adoption? Can we value all children, whatever their developmental potential? Can we stand with Sally Philips and others to embrace diversity even when it comes to our own children?

Krish Kandiah is father of six children, two of whom have a chromosome disorder. He is also a foster carer, and founder of Home for Good, a charity seeking to find loving homes for every child that needs one in the UK.