I keep thinking that if same-sex marriage posed such a threat, why isn't it clear to me or millions of others? We understand other obvious threats, such as disease or armed robbers or sour milk.

If gay marriage is so inherently threatening to society, and if we're telling the truth when we say we want to preserve that social order, why isn't the gay-marriage "threat" obvious? I grew up in the church; how come gay marriage doesn't threaten me?

Because it isn't a threat.