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."