If the MCCLRA Violates the Establishment Clause, Then Virtually All Laws Are Unconstitutional
If the fact that some support legislation for religious reasons makes the enactment of that legislation unconstitutional, then virtually all enacted legislation would be constitutionally suspect.
Consider, for example, the number of times in which ministers are brought in to testify in support of more politically liberal positions on issues like abortion rights, immigration, education, human sexuality, crime, and means and rates of taxation. Does their support for any legislation on those issues, if enacted, make that legislation constitutionally suspect?
Even organizations such as the ACLU and the Freedom From Religion Foundation make arguments for and against legislation based on their understanding of God/the Divine/the Supernatural and the relationship between those beliefs and proposed legislation. Consequently, enactment of legislation those organizations support would make those bills constitutionally suspect, too. “Religious” is a broad word, and it can’t be applied as if it’s a one-way street to an Establishment Clause violation only if the religious view is theistic.
But none of these more theological, philosophical, or metaphysical arguments should have any bearing on the constitutionality of the MCCLRA, because it rests on the existence of a relation recognized by common law, a privately-entered into (not government authorized) marital contract between a man and a woman.
What the U.S. Supreme Court Has Said About the Importance of Common Law to the U.S. Constitution
With respect to the common law, the United States Supreme Court has said:
[It]is the system from which our judicial ideas and legal definitions are derived. The language of the Constitution and of many acts of Congress could not be understood without reference to the common law.1
The interpretation of the Constitution of the United States is necessarily influenced by the fact that its provisions are framed in the language of the English common law, and are to be read in the light of its history. 2
[The Constitution] must be interpreted in the light of the common law, the principles and history of which were familiarly known to the framers of the Constitution. 3
Moreover, the relevance of the common law and its interpretative value relative to the U.S. Constitution is demonstrated by the Supreme Court’s high praise for and use of Sir William Blackstone’s Commentaries on the Law of England:
Sir William Blackstone’s . . . Commentaries on the Laws of England not only provided a definitive summary of the common law but was also a primary legal authority for 18th- and 19th-century American lawyers. 4
[Blackstone’s Commentaries] constituted the preeminent authority on English law for the founding generation. 5
Blackstone’s Commentaries are accepted as the most satisfactory exposition of the common law of England. . . . [U]ndoubtedly the framers of the Constitution were familiar with it. 6
U.S. Supreme Court Precedent Using the Common Law to Interpret the Constitution
Consistent with the preceding comments about the common law and Blackstone’s Commentaries, the common law was discussed and considered most recently in the majority opinions of the United States Supreme Court in Gamble v. United States (2019), to interpret the word “offense” in the Double Jeopardy Clause, and in Knick v. Township of Scott (2019) to discern the meaning of the word “taking” in the U.S. Constitution relative to eminent domain.
The common law has also been used to determine the meaning of the words “keep and bear arms,” as set forth in District of Columbia v. Heller, 554 U.S. 570, 128 S.Ct. 2783 (2008); the right to confront one’s accusers secured by the Sixth Amendment in Crawford v. Washington, 541 U.S. 36 (2004); the right to a jury for facts relative to sentencing in Apprendi v. New Jersey, 530 U.S. 466 (2000); the immunities recognized by the 11th Amendment in Alden v. Maine, 527 U.S. 706 (1999); and the word “crimes” relative to the right to a trial by jury in Bloom v. Illinois, 391 U.S. 194 (1968).
 Moore v. United States, 91 U.S. 270, 274 (1876), quoting Schick v. United States, 195 U. S. 65, 69 (1904).
 Smith v. Alabama, 124 U.S. 465, 478 (1888).
 United States v. Wong Kim Ark, 169 U.S. 649, 654 (1898), quoting and citing Minor v. Happersett, 21 Wall. 162; Ex parte Wilson, 114 U.S. 417, 422; Boyd v. United States, 116 U.S. 616, 624, 625; and Smith v. Alabama, 124 U.S. 465.
 Washington v. Glucksberg, 521 U.S. 702, 712 (1997).
 District of Columbia v. Heller, 554 U.S. 570, ___, 128 S.Ct. 2783, 2798 (2008), quoting Alden v. Maine, 527 U.S. 706, 715, 119 S. Ct. 2240, 144 L.Ed.2d 636 (1999).
 Schick v. United States, 195 U. S. 65, 69 (1904).