The very first phrase in the Bill of Rights (which gives us some idea of its importance in the minds of our Founders) is: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof;". Already this has been defined by the Supreme Court to permit a State to regulate the use of drugs as part of religious ritual, on the basis of "compelling state interest", while at the same time the Court says elsewhere that compulsory prayer in school is unconstitutional.
In one case the Court is allowing the State to regulate religious practice, and in the other the Court is telling the State it cannot impose a particular religious practice. This helps us see the basic parameters of the discussion - what is the relationship between the State and the exercise of religion. The First Amendment recognizes this dual role, for it first seeks to prevent the State from imposing religion (no law respecting the establishment of), and then seeks to prevent the State from prohibiting its free exercise. For a State-run school to require prayer violates the establishment provision, and yet the State does have the power to limit its "free" exercise, when there is a compelling State interest (ritual use of peyote, plural marriage etc.).
Any sociologist, or political scientist, worth his PhD knows that in modern life the so-called Christian Religious Right has been seeking to impose its moral views everywhere in American society, mostly by using the State's legal authority. This view of the Christian Right is not justified by any real understanding of the role and purposes of Law, or of the historic nature and ultimate development of the United States as the People of Peoples. America is not a mere Christian Nation, but is instead that most remarkable creation out of the Genius of History, of the first People in which religious, cultural and language differences could achieve a cooperative form of existence.
The Christian Right seeks to bring history to a stop, and to assert power over the American People in order to impose its own religious version of moral order.
This is actually an understandable position, for many places in the world are aware of what has to be called the almost violent pace of change. Our Age is a time of much too rapid change, as if the whole social and historical developmental process was racing out of control. The Christian Right sees this in what they originally called the "family values crisis" and what is now generally characterized as "cultural warfare". They understandably want to resist those cultural forces which might lead their children to travel paths outside their traditions.
This is nothing new in history, and certainly is true in far wider places than the United States. This same Christian Right, for example, while decrying the changes in the moral nature of America, seek to impose, through laws restricting our foreign aid from supporting abortion clinics or these same clinics from providing sex education to show people how to avoid aids, their own moral codes in the lives of other Peoples and Nations.
On the one hand they don't want the State to keep prayer out of schools, while on the other hand they want to use the power of the State to enforce moral rules inside our borders (no Gay civil rights such as equal protection) and outside our borders in what is a permissable use of foreign aid.
This is in no way a consistent position, in a rational sense, while it is an understandable position when people are faced with a too rapid pace of change.
Unfortunately it is a view which does not understand the nature of a Society, of the meaning of History, or the significance of Law within the struggle to create order. It is a view with a very narrow self-protective focus, that believes the best way to protect itself is to impose values on others, all the while complaining about the imposition of others values on it (cultural warfare).
For example, the Law is not meant to impose moral order on a Society, but rather to define the foundational rules below which Society will not tolerate behavior to go. Law is the lower border of expectable behavior, and moral behavior, by its very nature, is the upper border - the goal toward which we believe a human being can and should aspire.
Law, such as a Constitution, then is the product of a community process, within which everyone is meant to be equal - to have the same rights, and duties. Moral behavior is an individual process, by which one is guided by one's religion or philosophy toward ethical or conscience based activity.
We cannot afford to confuse the two. Yet, the whole nature of the political activity of the Christian Right is to do just that - create enormous confusion between Law and Morality. In seeking to impose a moral view on our Society's basic legal structures, by the Marriage Amendment, the Christian Right effectively wants to do an end run around the First Amendment, and actually build into the constitution a kind of irreconcilable difference.
What makes this all the worse, is that when you listen to the reasons put forth by the Christian Right and the Republican and (unfortunately) Democratic leaderships, that seeks to court their votes by following this disastrous plan, it is clear that the real motive is not to add something of value to the Constitution, but rather to impose through Law their own values on a minority.
In this abuse of majority power, the Christian Right demeans our legal processes, savages the fundamental nature of the Republic, and eviscerates the Bill of Rights., which exists precisely to prevent a tyranny of the majority.
All this is mostly driven, not by any rational process, but by a fear of too rabid change, Nothing good can come from this abuse of Law and of the basic structure of our form of Government. Morality is not the purview of the State, but rather of religious teaching and individual conscience. The State exists to hold us equal, and to protect the minority from the majority. If a religion can not inculcate its moral values through teaching only (without the abuse of the Law as a club of enforcement), then those values have no real meaning.
What this really represents for the Christian Right is a lack of faith. It is only from a position of weakness that one would seek to impose one's moral values on others. Christ's Teachings have no need of the application of such force of arms (the rule of Law), for their value is readily apparent to any human being of conscience. In seeking to impose through Law, these moral ideas, the Christian Right is no better than the Catholic Church of the Middle ages with its hate mongering torture chambers and burnings at the stake.
This then is the real driver behind the Marriage Amendment - fear of change and hate of Gays. The offered rationality of protecting marriage is a sham. Marriage is in fine hands already, and it is under no threat from those who seek to enter its sacred chambers wishing to sanctify their own love and desire for family. In fact, to confine the Sacrament of Marriage to just a man and a woman, is to place failure prone human limits on God's Love. This means that the Christian Right lacks both faith, and a real appreciation of the Love of the Creator. But the dimensions of that problem is a whole other discussion.

