The marriage amendment would not only be the first Constitutional amendment since Prohibition to reduce the rights of the people. It would also be the first ever to directly contradict other parts of the Constitution, namely, the Equal Protection clause of the Fourteenth Amendment and the Establishment clause of the First.

"Nor [shall any state] deny to any person within its jurisdiction the equal protection of the laws"

To the extent that the state recognizes or sanctions marriage in any legal sense, it cannot deny the benefits of that sanction to any person or group of people without violating Equal Protection. Private institutions, like churches, can choose not to perform same sex weddings, but the state cannot give legal standing to one type of marriage without giving the same standing to all types.

There is no basis for denying the marriage sanction to same sex couples except on the grounds of religious belief. Given that, the marriage amendment would write religion into the Constitution itself, which would be grossly at odds with the First Amendment. This would effectively destroy the time-honored separation of church and state, which serves to protect all religion from government interference.