PROVO — Legalizing same-sex marriage will have significant, long-term societal, fiscal and legal consequences just as smoking and divorce do, even among those who don't personally participate.

That's the assessment from Lynn Wardle, a professor of law at Brigham Young University, who encouraged an audience of attorneys at the school's annual Education Week on Thursday to speak out in opposition to same-sex marriage, rather than being silenced by fear.

"Legalizing same-sex marriage or civil unions endangers not only marriage as an institution but will endanger the civil rights" of those who don't approve of it, Wardle said. "It's about the right to express opposition, and those who do so already suffer harassment and hostility."

As one of very few law professors who speak publicly against it, Wardle said he's been screamed at during the proceedings of large and respected organizations. "I've been called homophobic by a state senator."

"Hate-filled, homophobic, narrow-minded and bigoted — those are the labels you'll get. Those of you who live in California, put on your armor," he said, referring to an upcoming ballot measure that would strike down a recent Supreme Court ruling there legalizing gay marriage.

"Those attacks are purely an effort to silence, harass and drive out of the public square those who oppose them," he said.

"That's the greatest concern I have, the effort to intimidate and silence those who have different views. I've had professors I greatly respect come up to me in dark hallways and tell me they agree with me, but they won't stand up in a meeting and say so. They're afraid of the criticism they'll endure."

Changing the core definition of marriage will lead to clashes between those who have religious views about marriage and those who don't. "Those who want to promote conjugal marriage will be targeted," and many already have been, he said.

Most people who hear much from same-sex marriage proponents but little from the opposition wonder what the harm is, Wardle said. "It's not like a bone sticking out of a limb or blood spurting out of a wound. ... It will be at least a full generation before all the consequences are known. Like smoking, it will take years and decades to see the result."

He likened the consequences to the effect of divorce on children, recalling debates on the subject when he was a law school student. The notion of harm to children "was resoundingly rejected ... everybody said it's tough initially but it will be OK and there will be no lasting effects."

Yet, within a decade social scientists began documenting very distinct harm to children, he said. "There is now a large body of irrefutable evidence of the serious, harmful effects for children of divorce that have been documented."

While the impact is "temporary for two-thirds, it is lifelong for about one-third," he said. Making same-sex marriage legal "will harm you and your family the same way polygamous marriage to 14 year olds will harm you. ... It will transform the meaning, expectations and practices of marriage as a social institution and affects everyone who has a stake in marriage."

Legalizing such relationships would affect the functioning of the entire legal system, he said, "from taxes to torts, from wills to medical treatment. The laws will change, and we'll reconceptualize our understanding that the union of two men or two women is equally important."

In doing so, taxpayers will incur "huge social costs," just as they do now when marriages fail. He cited a recent study by a business professor at the Institute of American Values putting taxpayer cost of marital breakdown and nonmarital childbearing at $112 billion per year.

"That's $70 billion in federal costs, $42 billion in state costs, and it amounts to over $1 trillion per decade. If you think fighting the war in Iraq is expensive, we've been paying those costs in this country for the past 30 years."

Estimates show those figures translate into about $4,500 per year, per family, in taxpayer dollars. "If your tax burden is high now, wait until those (same-sex) marriages fall apart and the state has to care for" divorced spouses and children of those broken unions, he said.

Traditional marriage "contributes much more to society than any other form of adult intimate relationship," and is the bedrock of "society's cultural infrastructure." It is the "instrument of the most important moral transformation of individuals," who enjoy the "most healthy, satisfying and socially beneficial sexual relations."

"Gay sex differs in critical ways," from that between husband and wife, he said, beyond the lack of offspring. "The major transmission method for the AIDS virus is through sex between men in every area of the world other than sub-Saharan Africa."

Wardle blasted the California Supreme Court's decision earlier this year legalizing gay marriage as "judicial legislation" that "weakened the most basic institution of society." The ruling was "based on assumptions that same-sex marriage contributes as much to society as gay marriage," and that notion is "not without consequences. They simply assumed the absence of harm and closed their eyes to contrary evidence. In fact, they refused to even examine it."

The ruling was a "bold and bad political act that lacked judicial care and caution, but rather opted to exercise political influence." It was an "act of arrogance seldom matched in American legal history" that virtually "guaranteed litigation will occur in other states."

He said the only real solution to continued legal wrangling over how individual states will interpret and adapt to same-sex marriage is amending the U.S. Constitution to define marriage nationwide. While advocates for same-sex marriage have made swift headway in the past 15 years, there has been measurable "push-back," he said.

"Those of you who are summer soldiers or weekend warriors" in speaking out on public policy, "please re-adjust your thinking. These issues are generational and we'll have to work at it for a generation or two. If we do, our grandchildren will reap the benefits of what we're trying to do."

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