Which ideas will endure for at least another century?" was one of the questions we were posed at a thought-provoking conference over the weekend. We considered and dismissed democracy – in the past century, it's been overthrown by communism, fascism and autocracy – and capitalism, which even now seems a little under threat. One concept, though, kept bubbling up into my mind: love.

Whether you worship the Beatles or the Bible doesn't matter. Love is either all you need or it's greater even than faith and hope, and all three will endure. It's the biggest contributor to human happiness, and if politicians dare to intrude into our love lives, they can have a more profound effect than any tinkering with taxes or the national curriculum. Which is why women and gay men should be deeply grateful that, in this era, we live in Britain and not the United States.

In this country, people have become increasingly freer to love whom they like and to live how they like. Tolerance of homosexuality in particular has blossomed in the past couple of decades, making the country strikingly more generous. It's been a really big and welcome cultural change.

As recently as ten years ago, there was no political consensus in the UK over gay relationships. The Tories under Margaret Thatcher had been actively hostile. The notorious Section 28 of the Local Government Act 1988, which banned local councils from promoting homosexuality, had been passed in protest against a book in a school library called Jenny Lives with Eric and Martin. The book told the story of a little girl, whose father Eric was gay, but whose mother lived nearby and visited frequently. It was a well-meaning attempt to help the few children living with a gay couple to feel that they weren't alone.

Jump ahead to 2002 and you still find a Conservative leader, Iain Duncan Smith, trying to whip his colleagues to vote against a law allowing gay couples like Eric and Martin to adopt a child. This time, though, eight senior MPs rebelled and the row marked the beginning of the end of Duncan Smith's leadership. By 2004, civil partnerships were passed into law by Labour with little opposition.

Now we have a Tory leader, David Cameron, saying he supports gay marriage not despite his Conservatism but because of it. And this week his Coalition Government is bringing forward proposals to legalise it. It is the most fantastic advance in the space of a few short decades. Gay couples who love each other, want to express that love in front of their family and friends, and are prepared to support each other through all the vicissitudes of life, will at last have the full backing of the law.

They will also have the backing of much of the British population. According to a YouGov poll for The Sunday Times yesterday, 43 per cent support gay marriage while 32 per cent support civil partnerships but oppose gay marriage. Only 15 per cent are opposed to both. There will be some hostility from the more traditionalist wing of the Tory party and shrill opposition from the churches. But this legislation, when it comes, will have broad support from all three main parties. And – like civil partnerships – within a decade or so the institution will seem as familiar and normal to us as any other.

Compare that with the US, where the presidential election campaign is blighted again by culture wars over sexuality and sexual behaviour. There, support for gay marriage is higher even than in Britain. Yet the issue is hugely politically divisive.

Among the Republican candidates, Newt Gingrich claims that a "gay and secular fascism" is trying to impose its values on the rest of the country and that "it's a very, very dangerous threat". He wants a constitutional amendment to prevent gay marriage. So does Mitt Romney. And Rick Santorum believes that even gay sex undermines "the basic tenets of our society and the family". So you can imagine what he thinks of gay marriage.

Republicans don't stop there. They are almost as obsessed with meddling in people's sex lives as the Church. For a country in which Church and State are supposed to be strictly separate, it's very odd how politicised the "morality" of sexual behaviour has become. I use the inverted commas because I don't believe sexuality is a moral issue at all unless it involves people getting hurt. Yet in America, the sex wars have now moved beyond abortion, which arguably is a moral issue, to areas like contraception and sex education. And they're taking the country backwards.

In Utah, a law bans sex education that mentions homosexuality, birth control and any sex outside marriage. Only abstinence is allowed to be taught. All four Republican candidates want an end to state funding for the Planned Parenthood charity, which – as well as providing abortions – prescribes contraception, cervical and breast cancer screening and infertility treatment.

Rick Santorum, as a Roman Catholic, disapproves even of contraception within marriage. And when Sandra Fluke, a law student, testified in Congress about government funding for birth control, against an amendment which would have allowed contraception to be excluded from health insurance, the conservative shock jock, Rush Limbaugh, described her as "a prostitute... who wants to be paid to have sex" by the US taxpayer. No mention, of course, of Viagra, which Limbaugh himself has used, and which is included in health insurance policies. For it's never heterosexual men who are targeted by the morality police. The victims are always women or gay men. This is a very selective morality that seems determined to maintain the dominance of men over women and straights over gays.

So thank goodness for a political culture here in Britain that allows the most private parts of our lives to remain private and cherished. Contraception is free and uncontroversial. Sex education is broadly sensible. Gay relationships are becoming ever more normalised. Political parties don't fight over sex. As a society, we are ever more at ease with the most important thing in life. And that matters a lot. For, as Philip Larkin famously wrote, reflecting on a stone-carved couple holding hands on a tomb that had lasted for many centuries, "What will survive of us is love."

m.sieghart@independent.co.uk / twitter.com/MASieghart