I didn't bring up Justinian, the man, I brought up the Code of Justinian. (Hint: there's also a difference between King James I of England and the King James Bible).
Justinian, James I, and George III were all comfortable with the concept of a state-sponsored religion. The United States was founded on the concept of freedom of religion.
Can you show me where the Code of Justinian is heavily influenced by Christianity? Aside from an article about the ownership of church property, and an aside about divine law, it seems to have little to do with the Mosaic Code.
The Decalogue is by all accounts "explicitly religious" and appears in the SCOTUS. So much for that argument.
Stylized depictions of the Tablets appear in artistic sculptures in the SCOTUS courthouse. You cannot read a single word of the Ten Commandments on display in that building that I am aware of. Furthermore, they are included to depict them many sources of law, and thus are placed there for a secular reason. If Moore had done the same thing his 'rock' would still be there. Instead he went out of his way to say that he placed the monument to establish Christianity as the official religion of the state.
From Book 1:
We desire that all peoples subject to Our benign Empire shall live under the same religion that the Divine Peter, the Apostle, gave to the Romans, and which the said religion declares was introduced by himself, and which it is well known that the Pontiff Damascus, and Peter, Bishop of Alexandria, a man of apostolic sanctity, embraced; that is to say, in accordance with the rules of apostolic discipline and the evangelical doctrine, we should believe that the Father, Son, and Holy Spirit constitute a single Deity, endowed with equal majesty, and united in the Holy Trinity."
"We order all those who follow this law to assume the name of Catholic Christians, and considering others as demented and insane, We order that they shall bear the infamy of heresy; and when the Divine vengeance which they merit has been appeased, they shall afterwards be punished in accordance with Our resentment, which we have acquired from the judgment of Heaven."
"Let no place be afforded to heretics for the conduct of their ceremonies, and let no occasion be offered for them to display the insanity of their obstinate minds. Let all persons know that if any privilege has been fraudulently obtained by means of any rescript whatsoever, by persons of this kind, it will not be valid. Let all bodies of heretics be prevented from holding unlawful assemblies, and let the name of the only and the greatest God be celebrated everywhere, and let the observance of the Nicene Creed, recently transmitted to Our ancestors, and firmly established by the testimony and practice of Divine Religion, always remain secure."
"Moreover, he who is an adherent of the Nicene Faith, and a true believer in the Catholic religion, should be understood to be one who believes that Almighty God and Christ, the son of God, are one person, God of God, Light of Light; and let no one, by rejection, dishonor the Holy Spirit, whom we expect, and have received from the Supreme Parent of all things, in whom the sentiment of a pure and undefiled faith flourishes, as well as the belief in the undivided substance of a Holy Trinity, which true believers indicate by the Greek word amounsioV . These things, indeed do not require further proof, and should be respected."
How's that?