Francois Lebel, the mayor of the capital's 8th district who married former President Nicolas Sarkozy and ex-supermodel Carla Bruni, has been widely condemned for his comments by politicians across the political spectrum.
But there are also growing signs of a grassroots revolt against gay marriage that could yet make life uncomfortable for the ruling Socialists as it seeks to enact the promised legislation.
Lebel, writing in a municipal newspaper this week, said lifting the taboo on same-sex marriage would set a dangerous precedent.
"Why then would the legal age for marriage be maintained? And why forbid marriage between close relations, paedophilia or incest which are all still common currency in the world."
Lebel's comments were condemned by Socialists from President Francois Hollande down and by leaders of his own party, the UMP.
Former prime minister Francois Fillon warned that Hollande's administration needed to tread carefully on the issue.
"They would do well to think twice before opening this debate now," Fillon said. "We are going to see the French people very deeply split over this issue."
Polls suggest up to two thirds of French voters back the right of homosexuals to marry but they are evenly split on whether gays should be able to adopt. Surveys also indicate that the issue is very important for those who are opposed to both reforms.
A group of mayors on the island of Corsica have announced they will refuse to carry out gay marriages and local councillors in the Paris suburb of Le Chesnay this week passed a motion calling for a referendum, an idea that seems to be gathering momentum.
The idea of a popular vote on the issue is backed by the Christian Democratic Party, an ally of the main centre-right UMP opposition, and by prominent figures in the Catholic church.
A draft bill covering both gay marriage and adoption rights is due to be approved in principle by Hollande's cabinet at the end of this month and the government has promised the legislation will be on the statute book by mid-2013.
Hollande has shown no sign of reneging on this manifesto promise despite backtracking on other elements of his socially liberal agenda.
With Hollande's blessing, Interior Minister Manuel Valls has postponed a promised move to allow residents of France from outside the European Union to vote in local elections and plans to make police officers keep a paper record of random identity checks have also been shelved.