SALT LAKE CITY — Eighty members of the Utah state legislature have filed a brief asking the U.S. Supreme Court to reverse a federal appeals court ruling striking down Utah’s same-sex marriage ban, because allowing gay to marry could lead to incestuous and polygamous marriages.

The amicus brief supporting Utah’s appeal asserts that the U.S. Court of Appeals for the Tenth Circuit “did not adequately consider the consequences of its decision for Utah’s prohibitions of polygamous and incestuous marriages.”

“If the choice of marriage partners is an unlimited fundamental right … and if that marriage choice cannot be denied even when a majority believes that choice to be ‘immoral,’ … then the fundamental rights analysis applied by the Tenth Circuit will apply with even greater force to consenting adults desiring polygamous marriage or marriage between at least some close relatives. The prohibition of those marriages has always been grounded in morality. “Without a moral justification, courts will be obliged to remove existing marriage prohibitions as the U.S. District Court did last month in Utah.”

The lawmakers also argue that “the State’s carefully crafted statutory scheme” of marriage as between one man and one woman best supports children: “The State definition of marriage maximizes the likelihood that a child will be raised by a married mother and father.”

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In December, U.S. District Judge Robert J. Shelby struck down Utah’s same-sex marriage ba n as unconstitutional. The ruling was upheld by the Tenth Circuit in June , which said states cannot deprive people of the fundamental right to marry simply because they choose a partner of the same sex.

Utah has appealed the ruling to the U.S. Supreme Court.

Last month, more than 60 conservative Texas lawmakers signed on to a similar brief filed in the Fifth Circuit in which they compare same-sex marriage to incest, pedophilia, and polygamy.

The Utah brief is here.