Cardinal Andre Vingt-Trois told a meeting of French bishops the planned marriage reform, which the government has speeded up amid mounting pressure from opponents, was a sign that society had lost its capacity to integrate different views.
Protests against the law, led by lay groups mostly backed by the Catholic Church, have become more agitated in recent days as noisy opponents rally outside the Senate and National Assembly and harass politicians supporting the reform.
Vingt-Trois, the archbishop of Paris, said the difference between the sexes was a basic human trait and denying it by legalising marriage and adoption for homosexuals would weaken society's ability to manage its differences peacefully.
"This is the way a violent society develops," he told the spring meeting of the French bishops' conference. "Society has lost its capacity of integration and especially its ability to blend differences in a common project."
The Socialist-led government, whose popularity has plummeted amid economic woes and a tax fraud scandal, is expected to pass the law next week to make France the 13th country to allow gays to tie the knot. Uruguay legalised gay marriage last week.
SIGNAL SOCIAL REFORM
The government decided on Monday that the law, one of the most important social reforms since France ended the death penalty in 1981, would be passed weeks earlier than planned and with a limited debate in its second reading.
Vingt-Trois accused the government of rushing the law through parliament without sufficient public debate.
"Forcing it through can simplify things for a while," he said. "To avoid paralysing political life when there are grave economic and social decisions to take, it would have been more reasonable and simple to not have started this process."
Opponents of gay marriage have staged three large protests in Paris, with over half a million demonstrators at their height. The last one in March ended in scuffles with police.
Since then, smaller groups have staged flash protests around Paris. Some 70 people were arrested on Monday after trying to set up a protest camp outside the National Assembly.
Others have harassed pro-reform politicians by noisily protesting outside their homes at daybreak or stalking them. Some held up a high-speed train due to bring government supporters from a conference in Nantes to Paris.
Rhetoric has heated up as well, with opponents accusing President Francois Hollande of being a dictator. "Hollande wants blood and he'll get it," protest leader Frijide Barjot declared in comments she later admitted "went a bit far."
Government leaders have accused the protesters of turning radical and criticised the increasingly frequent presence of aggressive far-right nationalist and traditionalist Catholic fringe groups at the otherwise peaceful protests.
All main religious groups in France, with the exception of the Buddhists, have spoken out against marriage reform.
Vingt-Trois said the main protest marches, attended by average citizens concerned about the reform's long-term effects, did not reflect the "religious, retrograde and homophobe mania" that some of their more vocal critics ascribed to them.
Same-sex nuptials are legal in 13 countries -- Argentina, Belgium, Canada, Denmark, Iceland, the Netherlands, Norway, Portugal, Spain, South Africa, Sweden and Uruguay -- as well as in some parts of Mexico, Brazil the United States and now New Zealand.
Several other countries, including Britain, are planning to legalise it in the near future.