Doug Mainwaring, a co-founder of the National Capital Tea Party Patriots, warned Tuesday that gay marriage will “undefine” children.

Mainwaring was among the speakers at the National Organization for Marriage's (NOM) rally on the Nation Mall calling on the Supreme Court to uphold two laws, Proposition 8 and the Defense of Marriage Act (DOMA), which exclude gay couples from marriage or from receiving the benefits of marriage.

“As a gay man, I can state categorically, it is not homophobic to oppose same-sex marriage,” Mainwaring told the crowd. “To the Supreme Court, legislators and jurists around the country: Slow this train down.”

In a previous essay, Mainwaring wrote that he dated men after divorcing his ex-wife. The pair have since reunited for the sake of their adopted children. But “because of my predilections,” Mainwaring wrote, “we deny our own sexual impulses.”

(Related: NOM promotes views of gay man opposed to marriage equality.)

“Same-sex marriage will not redefine marriage,” Mainwaring said. “It will undefine it. And unravel it. And in so doing will undefine children. This is not progressive legislation, this is regressive.” (The video is embedded on this page. Visit our video library for more videos.)