Dustin Lance Black was a screenwriter, living in Los Angeles, in demand and extensively garlanded, when in 2013 he met Tom Daley, the Olympian diver from Plymouth. Black was the ultimate progressive all-rounder – then 39, he had won an Oscar for Milk, a biopic of the assassinated gay rights activist Harvey Milk, and built a reputation for his activism on gay marriage. He was also known for the thoughtful, open manner of his pioneering: his narration of the awardwinning documentary 8: The Mormon Proposition was informed by his experience of growing up gay in the Church of Jesus Christ of Latter-day Saints.

So, when he fell in love with the diver – who is 20 years his junior and was then studiously neutral on politics, in the way athletes often have to be – it was not obvious from the outside that they were made for each other. Yet in the world where celebrities are still people, it was obvious to them. I have interviewed Daley, too, and he told me he introduced Black to his entire family and his friends in the week of their first date. They moved in together in London in 2014, got married in 2017 and this year had their first child.

Black – handsome like Christian Slater, wholesome like Nigella Lawson – is slightly too Hollywood to be congruous. He is exquisitely thoughtful and unassuming (“I’ll turn these carols off; they take me back to particular times and I don’t want to be thinking about my mother when I should be listening to you”).

While the scene is picture-perfect, right down to their outrageously cute baby, Robert Ray, who smiles even when he is asleep, Black is not an anodyne person. He is deeply political, undeterred by controversy or challenges. This is how he has come to make a podcast, Surrogacy: A Family Frontier, for BBC Radio Five Live (the first two of six episodes are available now). “When we announced that our surrogate was pregnant, in the US there was just a lot of congratulations. Here it was more mixed; it made people uncomfortable. So, I was really interested in what was going on.”

The series follows the whole spectrum of views around the matter – couples, surrogates, children born of surrogacy, anti-surrogacy activists, agents, lawyers – and is confronting. It defies any casual judgment: you could not listen to the relationship between a mother and her surrogate and say the process had done anything but enrich lives on every side. Yet every now and then there is a trenchant statement – “That’s not her baby: she was babysitting,” one expert says of a surrogate, while another explains that a surrogate could not possibly have a maternal bond with the baby because it is not her genetic material – which seems at odds with a primal human truth. Your body does not care whether you have signed a contract.

Facebook Twitter Pinterest ‘We didn’t want to know anything! We just wanted to have a baby’ ... Black with his husband, Tom Daley. Photograph: Paul Grover/Rex/Shutterstock

There is a distinction between traditional surrogacy, where the surrogate is also the child’s biological mother, and gestational surrogacy, also called “host” surrogacy, where she has the full embryo implanted and thus no biological relationship to it. The latter, which is what Black and Daley did, is much more common now, mainly because many agencies offer only that. “The traditional surrogacy process can be more legally and emotionally complicated,” one agency notes on its website.

A huge body of objection to surrogacy comes not from feminism but from homophobia. Earlier this year, Black made a radio show about their son, with a call-in at the end. “The last guest I had on that show was a gay man; he and his husband had kids,” he says. “All the calls that came in after that were homophobic. The anti-surrogacy calls were completely dispensed with – and there were real concerns: what happens to the surrogates, how are the children on the other side of it? ‘You shouldn’t have two dads or two mums,’ is what we were left with.”

Black and Daley got the brute force of this right from the start, when Richard Littlejohn wrote a poisonous column in the Daily Mail headed: “Please don’t pretend two dads is the new normal.” “We were in America when that came out and we said: ‘How are we going to deal with this?’ Neither one of us are angry people. I was on the frontlines of marriage equality for half a decade, so I know what it is to fight for what you care about. But we soon came to the conclusion that the way to address this unexpected reaction was to shed as much light as possible; meet anger and hate with curiosity.”

As in a lot of debates where people feel emboldened to weigh in on a stranger’s choices, the voice of bigotry is so much louder than anything else that you can forget what else there was. Black says: “There has been this resurgence in anti-LGBT language in the UK, and the US, and the rest of the world. In the US, we’ve heard it with Trump’s rise. Here, I’ve heard language borrowed from the most conservative anti-gay voices in the US used by some gay and lesbian people against trans people.” I tell him it feels like a tapeworm that you thought you had removed. He says: “Yeah, if we’re going to run with this hideous metaphor, we hoped the tapeworm had been excreted. But then we came to find out unspoken homophobia felt empowered to raise its voice again.”

This affects gay people’s ability to parent in all kinds of ways. In US adoptions, Black says, some states have a law that allows any biological relative of the child who objects to the adoption to nix it within a certain time frame. So, a gay couple can find the grandparents of their child suddenly reclaiming it, even up to a year after the adoption has been finalised. This narrows the options to surrogacy and perhaps explains why US law is so much more developed than ours in this area. The contracts are an inch thick. Everyone involved has a psychological, financial and medical screening. It is almost impossible to go into surrogacy in the US for reasons of financial desperation. “That’s the only way to ensure that women aren’t being taken advantage of. The podcast goes into how that chain of it being just for profit can lead to women being exploited – by their husbands, by their families – in more patriarchal societies. That can really lead to no good.”

In the UK, it is illegal to profit from surrogacy, although there is no architecture around it and no contract is legally binding. “Reasonable expenses” are allowed, but unclear in their extent, and there is no screening requirement. It is illegal to advertise for or as a surrogate, but that is a precaution that clearly predates social media. It is possible to go on Facebook, find a surrogate, agree your own terms and proceed from there – as one couple did on the podcast. “That story, to me, was a cautionary tale. The drive to be a parent is strong. It’s one of the most ingrained human traits there is. Well, then – we better have strong law to make sure that people can’t take advantage of others who are trying to do that. I do not like how that couple went about it. You would think as a gay man I would just be happy for them, but they walked through a minefield and took a child with them and I don’t think it’s right.”

With Robert Ray, Black and Daley used a US egg donor and a US surrogate; the absence of law in the UK makes it too much like “the wild west”, Black says.

When we announced our pregnancy, in the US there was just a lot of congratulations. Here it was more mixed

I say to Black that I have been thinking of the surrogate in that scenario. The only way you could make sense of carrying a child you were not going to keep would be on entirely altruistic grounds. Money would be no match if you ended up feeling that the child was yours. A surrogate going in on a gun-for-hire Facebook basis might end up in absolute despair.

“Do you know how many people in the US, having passed all the financial and medical tests, then pass the psychological one?” asks Black. “Two per cent. These surrogates are very unusual people – there is an altruism, there is an understanding of family and wanting to pass that along, there is a generosity of spirit, there is a joy in building family for others. And there is a certain kind of woman that can do this and not have those feelings … I would make a lousy surrogate. I get emotionally attached to someone if I talk to them on the street corner for five minutes.”

That, I think, is at the root of the UK’s unwillingness to tighten the law: surrogacy is a challenging proposition. A surrogate must care deeply for others and their happiness, yet cannot become attached to the baby to whom she will give birth. You have to trust that such people exist, based on their own testimony. But it is hard to build legislation around this idea.

Another couple in the podcast have a thing about “drive” – they want a baby with oomph, with the desire to get along in the world. Black delicately raises the idea of the “designer baby”. In real life, he says, this could never happen. “The doctor won’t tell you those things. They’ll tell you the gender, because that’s evident. They’ll do basic chromosomal tests to make sure they’re healthy. But good luck to anybody trying to guess what their child’s going to turn out like.”

It is always treated with a bit of suspicion, choosing sperm or eggs from a donor by going down a checklist of their exam results and how tall they were. Pot luck is part of parenting, the argument goes: you demonstrate the unconditionality of your love by the fact that you do not mind how they end up; if you do mind, you are not loving. I think this is specious: people are much more picky about mate selection than they are about donors.

Whatever the framework, you cannot keep emotions out of surrogacy. “I would say – this is not scientific, but close – what happened to us is what happens to 99% of people: you fall desperately, deeply in love with your surrogate.” (Their egg donor, likewise, although she has not hung out with Robert Ray, is deeply important to the couple, and not just because their son might want to meet her one day.) Speaking of their surrogate, he says: “We talk daily, we send pictures, not just about him, about anything. It’s not a nine-month process – a year and a half you spend with this person, building this thing that’s so meaningful to you. It’s incredibly bonding.” That is another part of the surrogacy contract: deciding how much contact you will have afterwards. Some people want very little, others want it lifelong.

Most prospective parents doing surrogacy are straight, so there is little confusion about whose genes are whose. When it comes to gay men, Black says, usually sperm from both partners is used to fertilise a number of donor eggs, with any embryos that are not implanted straight away frozen for later use. “You do half and half. The doctor always knows whose is whose and always knows the gender. Tom and I didn’t want to know.”

Whose he was or the gender? “We didn’t want to know anything! We just wanted to have a baby. The doctor knows whose sperm, because I always figured, when our son is ready, if he really is dead set on knowing, he needs to know everything. But we have more embryos. If and when we’re ready to move forward again, we can say: ‘Hey, whoever’s isn’t this one, use that one.’ I, frankly, would be whispering in the doctor’s ear, saying: ‘Use Tom’s – he’s so cute. He’s an athlete. The last thing you need is another writer.’”

The series – which is detailed, human and understandable in many ways – has left me more confused about surrogacy. Is the maternal bond overblown? Is it possible to see a pregnancy differently when you know it is for someone else? Does it really make any difference if the genetic material is not yours? Can altruism override more elemental impulses? Has the market interceded where it does not belong, with its contractual obligations and its screenings and its reasonable expenses? Have science and modernity overcome old impossibilities?

Black’s podcast opens up the space to ruminate, but there are no easy certainties. As for their child, there is no uncertainty: “He’s going to know where he came from. He’s going to know it took two very special women to bring him into our family. He’s going to have every right and opportunity to meet and hang out with them. He’s going to know who he is and where he came from, so that there’s no opportunity for shame in his life. I hope we build a son who’s strong enough to stand up for other people. And if Donald Trump is out there teaching folks how to build walls, we’re hoping to instil in our son the ability to know how to take them down.”

The first two episodes of Surrogacy: A Family Frontier are available online at BBC Sounds and available to download now on BBC Radio 5 Live’s website.