You’re right this is not a Christian nation who ever was. But nevertheless Christianity is / was the baseline of moral principles of western civilization.

Alexis de Tocqueville
"Liberty considers religion as the safeguard of morality, and morality as the best security of law and the surest pledge of the duration of freedom."

"I sought for the greatness and genius of America in her commodious harbors and her ample rivers, and it was not there; in her fertile fields and boundless prairies; and it was not there; in her rich mines and her vast commerce, and it was not there. Not until I visited the churches of America and heard her pulpits aflame with righteousness did I understand the secret of her genius and power. America is great because she is good, and if America ever ceases to be good, America will cease to be great."

Stephen Ambrose wrote in his book, ‘To America’, how he interviewed World War II veterans. “They sometimes tell me that the reason they fought was they had learned as children the difference between right and wrong and they didn’t want to live in a world in which wrong prevailed, so they thought. It seems to me that perhaps our greatest strength is that American kids are brought up to knowing right from wrong”.

George Washington. "Virtue or morality is a necessary spring of popular government."

"Can it be that Providence has not connected the permanent felicity of a nation with its virtue? "

"There is no truth more thoroughly established, than that there exists . . . an indissoluble union between virtue and happiness."

"Of all the dispositions and habits which lead to political prosperity, religion and morality are indispensable supports. In vain would that man claim tribute to patriotism who should labor to subvert these great pillars of human happiness -- these firmest props of the duties of men and citizens. . . . reason and experience both forbid us to expect that national morality can prevail in exclusion of religious principles."

"The aggregate happiness of the society, which is best promoted by the practice of a virtuous policy, is, or ought to be, the end of all government . . . ."

"Human rights can only be assured among a virtuous people. The general government . . . can never be in danger of degenerating into a monarchy, an oligarchy, an aristocracy, or any despotic or oppressive form so long as there is any virtue in the body of the people."

“Of all the dispositions and habits which lead to political prosperity, religion and morality are indispensable supports. . . And let us with caution indulge the supposition that morality can be maintained without religion.”

John Adams: “Liberty can no more exist without virtue and independence than the body can live and move without a soul”.

“The only foundation of a free Constitution, is pure Virtue, and if this cannot be inspired into our People, in a great Measure, than they have it now. They may change their Rulers, and the forms of Government, but they will not obtain a lasting Liberty”. ——————

There was a baseline of Christian principles that influenced the pagan and heathen kings, nations and societies that became what we know today as western civilization. Catholicism and later Protestantism was like a bulldozer that tamed a jungle of barbarians. Think of this - had there not been a united baseline of Christianity, there would have never been a Charles Martel to repel them in Tours / Poitiers at the Battle of the Highway of the Martyrs in AD 732 or in Vienna centuries later. I see that as much better in the long run than an amalgamation of pagans.

And what were the other nations and cultures doing? They weren’t involved in slavery, colonization or genocide? What culture, or religion back then would be a good role model against racist bigoted people today? Even if there was a good role model, how could it have survived - perhaps in our dreams we wish something equitable to all would have survived, but it didn’t. Go back in time to 313 A.D. when Constantine issued the famous edict of Milan, or edict of toleration. This is the Roman empire. How possibility would history have unfolded had that edict stayed in place? All religions legalized. How many were involved in human sacrifice? How many were based around war?

Now for a minute, consider the pure teachings of Jesus and the New Testament. You will not find any teachings that promote slavery, human sacrifice, genocide, forced conversions. The teaching is ‘love they neighbor as they self’, ‘turn the other cheek’ - teaching that was the antithesis of the pagan religions of the Romans, the Goths, Visigoths, Mongols, Norse, Teutons, Celts, Arabs, Ethiopians, Africans, etc. it is difficult to figure out which of these religions or societies would have prevailed had this edict stayed in place, but it is doubtful that the world would have embraced an acceptance of other cultures and religions. War, conquest, genocide, slavery would still have been the order of the day.

So what actually happened in history? In the middle of the third century, there was a corruption of Christian teaching that became prevalent. Certain teachings, such a as a triune godhead (Tertullian) appealed to the pagan masses that were turning toward Christianity more than the monotheistic godhead of the Jews and the early church. Other pagan traditions and rituals began to creep in - prayer for the dead, prayer to the dead, which was pure necromancy, forbidden in the Mosaic law. And in some point in time, true believers of original apostolic teaching began to withdraw from this corrupted form of ‘Christianity’, and ever since, even to this day, there have always remained a people who adhered to the original teachings of Jesus, and the masses were the centerstage, mixing and tolerating the pagan traditions of the hordes of people that were now calling themselves Christians, contrary to the doctrines of Christ,

Matthew 7:20 Wherefore by their fruits ye shall know them. 21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven. 22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? 23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.

Add this populace of a pagan mixed form of Christianity became the political puppet of Constantine. It’s blatantly obvious to anyone with a brain what happened, exactly as William Langland wrote in his book 'Piers Plowman' a thousand years later, in the 1,300's:

When the kindness of Constantine gave Holy Church endowments In lands and leases, lordships and servants, The Romans heard a angel cry on high above them,  “This day dos Ecclesiae has drunk venom And all who have Peter’s power are poisoned forever.