How do you help primary schools talk about same-sex relationships in a way that the Conservatives will support? That was the question Ruth Hunt, now Stonewall chief executive, posed when she hired me in 2010.

The answer is surprisingly simple: relate it to what children already know. They know some of their classmates have a mum and a dad, or just a mum, or foster parents, and that some children (some 20,000 in fact) are raised by two mums or two dads. We designed a series of posters depicting different cartoon families that were then sent to every primary school in the country. The result? Children in schools that used the posters didn’t bat an eyelid. Parents, including Muslim parents, from schools using the posters in Tower Hamlets, told us that, whatever their personal beliefs, they knew their kids needed to learn about the reality of modern Britain. As for the newly elected Conservative government? The posters received the personal backing of Michael Gove.

This was a far cry from my experience growing up. I started to realise I was attracted to men towards the end of primary school and was terrified. When I started secondary school, section 28 was still law. I vividly remember a teacher saying to us that she wanted to talk about gay people, but that it was against the law for her to do so. As a result, my early introductions to gay life came from surreptitiously watching Queer as Folk in bed.

My experience wasn’t unique. Which is why it’s so important that young people do now learn about same-sex families in primary school. To reassure those who may be coming to terms with their sexuality that there is nothing wrong with them. And to head off homophobic bullying before it starts, by making sure all children know same-sex relationships are just another of the many variations of family life. What that doesn’t mean is talking to young children about sex. It’s high time we disabused the notion that being gay is just about sex. It’s about telling children that some families have two mummies or daddies and there’s nothing wrong with that.

Consultation is key, but you cannot negotiate on the existence of LGBT people

Nor does it mean telling children their religious beliefs are wrong. Many faith schools show that it is perfectly possible to teach about same-sex relationships and remain true to the tenets of your faith. For instance, teaching that in Catholicism marriage is between a man and a woman, but in Britain same-sex marriage is the law of the land. Nor does it remove the need for dialogue between schools and parents. It’s obviously better to bring parents with you and in the vast majority of cases once parents see quite how tame the materials are, their concerns are quickly assuaged.

The sad thing is that I had assumed all of this was a given. But the campaigners protesting against the No Outsiders programme in Birmingham have accused Parkfield school of “planting the seed that homosexuality is morally fine”, a worrying echo of the words of Jill Knight, lead parliamentary sponsor of section 28, who justified the legislation saying: “I was contacted by parents who strongly objected to their children at school being encouraged into homosexuality.”

Even more scary is how quickly this single parental protest has snowballed. In desperation, a number of schools including Parkfield have suspended their inclusive relationships teaching entirely. And, in perhaps the most startling rebuke to those of us who thought that the fight for LGBT equality was won, in the past week both the BBC’s Woman’s Hour and Question Time have felt it appropriate to debate the “morality” of discussing LGBT issues in schools. In the midst of this, we can take heart from the fact that MPs voted 538-21 in favour of new guidelines endorsing LGBT inclusive relationships education. But it is worth remembering those guidelines are permissive. They leave it to the discretion of the headteacher in consultation with parents. Parkfield’s example shows us that risks leaving heads exposed in our new culture wars.

Amanda Spielman, Ofsted’s chief inspector, has given her full backing to inclusive relationships education. But schools such as Parkfield need more allies. This isn’t a time for trying to split the difference. Consultation is key, but you cannot negotiate on the existence of LGBT people. We wouldn’t dream of doing it for any other minority group. Last week’s vote on inclusive relationships education will mean nothing if we don’t challenge those who are deliberately exploiting parental concerns to advance a homophobic agenda. What’s at stake isn’t just what’s being taught in one school, but all of the progress we’ve made towards making this country a fairer, more equal and more open country for LGBT people. That’s worth defending.

• Luke Tryl is director of the New Schools Network, a former special adviser to Nicky Morgan and head of education at Stonewall