The bishops of Massachusetts’ four dioceses have jointly condemned a web-based dating service catering to those already married, which is seeking to expand its membership into the state through an advertising campaign.

“We, the Roman Catholic Bishops in Massachusetts, as pastors and teachers, are compelled to speak in support of marriage in light of a recent advertising campaign promoting adultery in the Commonwealth,” said Cardinal Sean P. O’Malley, the archbishop of Boston, Bishop George W. Coleman, the bishop of Fall River, Bishop Timothy A. McDonnell, the bishop of Springfield and Bishop Robert J. McManus, the bishop of Worcester.

The bishops’ joint statement was issued through the Massachusetts Catholic Conference, the public policy arm of the Church in the Commonwealth.

“The ads encourage the use of an online dating service for married persons contemplating adulterous relationships. This wrongful enterprise threatens not only the oldest and most foundational of human institutions but also the common good of all,” the bishops said.

In addition to the damage done to the institution of marriage by the Web site and its commercials, the site sends the wrong message to young people, they said.

“Where marriage is weakened the social cost is enormous. We commend those media outlets that have refused this advertising and ask that other media outlets do the same,” they said.

The Web site, AshleyMadison.com was started in 2002 based on the premise by Darren Morganstern, who co-founded the company with Noel Biderman, that if 30 percent of the users of on-line dating services were in committed relationships, a business could be developed focusing on that niche, said Biderman.

Biderman is the site’s president and the CEO of its parent company, the Toronto-based Avid Live Media.

Biderman said he was aware of the statement from the Massachusetts Catholic Conference and prefers to respectfully disagree.

“The Catholic Church is in no position to make a judgment considering the trouble they got themselves into with the improprieties with their clergy,” he said.

“I have found that the people who scream the greatest are the ones in the most trouble. The Catholic Church is losing people in droves trying to make people follow archaic and mundane rules or definitions of marriage,” he said.

Whether the site exists or not, people in Boston will have affairs, he said.

Adultery is still against the law in Massachusetts, said Robert H. Quinn, a former state attorney general and a founding partner of the Boston law firm Quinn & Morris.

If a Web site could be shown to aid in the commission of a crime, it could be vulnerable to charges itself, he said.

Quinn said the state’s Supreme Judicial Court in 1983 validated and affirmed the laws forbidding adultery as not affected by privacy rights derived from the Supreme Court’s 1965 Griswold decision.

However, in the same opinion the court noted that the laws, while still in force, are rarely enforced, he said.

Biderman, who is also an attorney, contrasted the letter of the law with its application through jurisprudence.

Biderman contended that, regardless of what laws are on the books, adultery is not illegal in Massachusetts.

“I defy anyone to show me anyone who has been charged with adultery, let alone convicted and incarcerated. If a law is universally ignored, it is no longer valid,” he said.

The Church teaches that adultery is a violation of the sixth commandment. In the “Catechism of the Catholic Church,” adultery is listed as an “offense against marriage” and described as “sexual relations--even transient ones” outside of one’s marriage.

Adultery is further described as an injustice against the marriage covenant and the “good of human generation and the welfare of children who need their parents’ stable union.”

“The media reaction in Boston has been more unique than any other city we have entered because individuals in the Boston media have depicted our coming to Boston as a reflection of the personality or behavior patterns or religious beliefs in the city,” Biderman said.

There is only one Web site, but the company drives up registrations from different markets through its marketing, he said. The decision to market the site in Boston was made in September, first with direct mail and then with radio ads.

“So far, tens of thousands of Bostonians have taken advantage of our service,” he said. As of the third week of November, the number of Boston-area registrants was more than 30,000. The site has 2.7 million users in total.

“Boston is a unique market, but it is not any more unique than New York or Los Angeles, where we are already,” said Biderman.

In every market there is resistance from media outlets, but nothing like what happened in Boston, when WBZ-TV, a CBS owned outlet, cancelled a signed insertion order, or contract, for an ad buy, he said.

“If I was a shareholder in CBS, I would be furious, considering that they turned down tens of thousands of dollars that we wanted to pay them. The last time I looked that company is losing millions of dollars,” Biderman added.

Biderman said the cancellation was hypocritical because the same station will air commercials for alcohol, erectile dysfunction and even for Las Vegas tourism, which encourages both gambling and other behavior some consider immoral.

To date, the site is advertising on radio stations WBCN and WAAF, and expects to complete major buys in January, including television, he said.

The director of communications and public relations for WBZ-TV, Ro Dooley Webster, said no one at WBZ-TV signed paperwork that would have bound the station to air the commercial.

“It is routine for our sales department to discuss ad requests, which are then evaluated by our standards and practices department,” she said. “As one can expect, this ad did not pass muster and was rejected.”

Webster said although WBCN is owned by the same parent company, CBS, the radio station division operates independently from the television station.

Binu Koshy, Ashley Madison’s director of marketing, said he is confident the downturn in the economy will eventually lead a local Boston television station to carry his advertisement.

“Let me put it this way: in January 2008, there was not a single terrestrial television that would even talk to us. Now, I get four or five calls a day, just from television stations,” he said.