By Duncan Kennedy
BBC News, Mexico City
When Mexican pop band RBD sang of love with their hit Tu Amor (Your Love), few took its lyrics to be about anything other than affection between a boy and a girl.
But when lead singer Christian Chavez announced recently he was gay it was about as shocking as hearing that Mick Jagger had decided to enter the Eurovision song contest.
It has taken years for same-sex unions to be accepted in the capital
In this deeply-conservative society, he had metaphorically pulled the pin on the pop grenade.
Being openly gay in Mexico is a challenging experience.
Not long ago, I was getting my shoes polished in a row of pavement shoe shiners. Two men walked past hand in hand. Practically every one of the shoe shiners looked up from their polishing, to sound off a dismissive whistle at the couple.
Yet it is believed that in this country of nearly 100 million people there are around 10 million gay and lesbian people.
And now the capital city has finally recognised the phenomenon. It is allowing same-sex civil unions. Not quite marriage, but official acceptance of a relationship between two men or two women.
"It is simply fantastic," says Julio Roman, a gay rights campaigner in Mexico City.
"It is more than symbolic," he adds. "It is the result of years of fighting for our basic rights."
Seven years in fact. A long struggle for those who defend and promote such unions.
Unlike national governments, cities in Mexico tend to be run more by left-wing parties who take a more liberal view on social matters. But even in the capital, convincing doubters has been difficult.
And the rise of this "urban permissiveness" is not pleasing everyone.
Catholics and other Christians have taken to the streets to voice their objections.
"It is simply not the will of God to have acts of homosexuality," says Armando Martinez Gomez, president of the Association of Catholic Lawyers.
"We are not against gay people," he adds. "But we believe in a union between a man and a women for the creation of children."
The fears of many Catholics in Mexico go deeper than concerns about civil unions.
They also believe that such unions are a prelude to an attack on other deeply held moral beliefs.
Already there is a campaign to modernise the country's abortion laws. After that, they say, the laws on euthanasia will come under pressure.
Christian Chavez was applauded by many when he came out
Supporters of civil unions say they do not have a shopping list for wholesale change, a cherry-picking agenda aimed at uprooting the social and cultural certainties of Mexican life.
But when pop prince Christian Chavez came out and declared his homosexuality, many applauded him for rejecting the country's rigid, conformist, ways.
Latin America is changing.
It is coming more into line with some states in the United States and some countries in Europe.
Buenos Aires, Argentina's capital, has legalised same-sex unions. So too has a state in southern Brazil.
Some say same-sex civil unions are about civil liberties, others that they are anti-family.
Morality and legality, ancient themes but with familiar divisions.