One weekend after demonstrators staged rallies in more than 80 cities to show support for the legislation, a large crowd packed Rome's Circus Maximus ruins to express the opposite view.
"We are here in Rome to defend the family, not only our family but all the families in Italy and all the families in the world," Armando Mantuano said. "I hope that we defend the children, because they deserve a father and a mother."
Mantuano had plenty of company. Organizers claimed more than 2 million in attendance; a survey of the crowd suggests a far lower figure, perhaps tens of thousands, though no official figure was immediately released. Their hope was to influence legislators ahead of next week's parliamentary debate on the proposed law.
Every other major Western European country already has legally recognized same-sex partnerships -- civil unions or marriages -- and corresponding adoptions. But it's no sure thing this will happen soon in Italy, a country with deep Catholic roots.
Saturday's crowd, consisting of everyone from nuns to small children, listened and often cheered as speakers talked about their desire to keep marriage between one man and one woman. They were often even more adamant about not letting homosexual couples adopt children, with organizer Masimo Gandolfini decrying what he called "the sale of a uterus."
"A woman is not a furnace where children are made," Gandolfini said. "And you cannot transform parenthood into a right."
Alessandro Margiotta, a doctor, woke up at 5 a.m. to travel all the way from Rimini to Rome to join the throng and drive home this point.
"We want to say 'No' to ... civil unions," Margiotta told CNN. "[And] we think [children] have the principal right to have one mother and one father, not two fathers or two mothers."
Gay couple taken back by debate
One distinct possibility is that the existing legislation is split up. That could mean allowing legal recognition of same-sex couples for taxation and other purposes, but not to let them adopt children, which is driving some of the fiercest opposition.
Revising the law in this way would be no comfort to Dario De Gregorio and Andrea Rubera.
They were married in Canada in 2009, and both their names are on the birth certificates of their three children, all of whom were born thanks to a surrogate mother, anonymous egg donor and both of their sperm. Their hope now is to have officials in Italy, where they now live, recognize both men as their children's parents, not just one or the other.
Rubera has been taken back by the venom that's been directed against gay and lesbian couples amid the debate.
"They portray us as robbers or kidnappers, using words like 'womb for rent, uterus for rent,'" he told CNN. "Saying you stole your kids, you stole your kids from their mother. You denied to your kids to have a mother, you bought your kids from the supermarket like watermelons."
He's hopeful that Italy passes the proposed law but resigned to the idea that the country is not yet ready for full-on same-sex marriage.
"I think we have to fight in the future for equal marriage," Rubera said. "But at the moment, I think civil unions would be a good first step with stepchild adoption."
In the Catholic Church's backyard
While there's no denying the gay rights movement's momentum elsewhere in Europe, Italy is a unique case because of its position as the cradle of Roman Catholicism.
Around the world, the Catholic Church has been among the most outspoken entities in support of traditional marriages and opposition to those between two men or two women. While Pope Francis hasn't weighed in personally on Italy's debate, it is notable that his Church's headquarters, the Vatican, is literally surrounded by Rome.
The Italian Bishops Conference on Friday ripped the idea of "alternative" marriages, its president Angelo Bagnasco having said earlier that "we must never forget the identity that is proper to the family."
Yet Nunzio Galantino, that conference's secretary-general and a close ally of Pope Francis, had adopted a softer tone.
"Society has in itself an increasing presence of different kinds of couples," Galantino said in a statement. "The State's duty is to give answers to all, with respect to the common good, above and beyond the welfare of single individuals.
"We are all learning that when confronted by such a complex reality as this, if positions are radicalized, whatever the good will, one ends up with fragmented and disorderly solutions which are often the product of the prevailing of one lobby over the other."