Not analogous. Free Republic is a forum. The MD borders on being a statement of faith.
I think the Declaration of Independence is in some ways comparable to the Manhattan Declaration: something written for secular purpose, but in the context of Faith, uniting many men --- different though their churches may be --- to face a present crisis.
One important point of comparison is that the principles we are talking about in both documents, are principles that can be defended by Natural Law.
It is a category mistake to critiquing the Manhattan Declaration as if it were a church document. It is not a church document. It is a statement made by people from widely different Christian churches about aspects of the present cultural/political crisis.
I greatly admire Albert Mohler, for example, an eminent Baptist, for signing the statement, but I don't expect him to vary one iota from his opposition to some aspects of my Catholic church, creed and theology.
That's why the Manhattan Declaration couldn't be, in a comprehensive sense, a creedal statement. It is a statement about the clear and present danger with regard to the killing of unborn babies, the legal mainstreaming of sexual perversion, and our obligation in conscience to defend what is right and just.
Politics is a lesser thing than the great theological virtues of Faith, Hope, and Love. But it can be in harmony with Faith, Hope, and Love. Public justice is subordinate to, but in harmony with, the very love of Christ our Lord. The Manhattan Dec, like the Declaration of Independence, like Free Republic, should help us work together. That's what I'd like to see more of in the coming year.
A happy New Year to you, guy! And may you flourish and be blessed by Him who made you for Himself.