What Christians accept as a moral code was not invented by them. It exists elsewhere as well.
Well I guess it depends on what and where you are referring to. When we think of morality in a modern society we have to look at the historical influences upon that society. Christianity has has less of an impact in India and China for example than in Europe and the United States. It's not surprising that the moral standards of society are slightly different as a result. The United States was based strongly in Protestant Christianity. People fled Europe to come to the New World in order to freely practice their religion. They brought with them their moral codes which in many cases have been passed on to the present day. Over time the norms and mores of society evolved according to several factors and historical events but have remained generally Christian in nature. Even atheists, who often claim that their moral code is not based in religious belief, are subject to the definition of morality according to society and the Christian history of the United States. In other words, they may not believe in God, but their view of morality is still influenced by religious belief because it was religious belief that established the standards for moral behavior in society over the centuries.
Before Christianity, the Roman Empire was a brutal and ruthless society in which law enforcement engaged in the most horrendous acts and in which the people enjoyed the spectacle of people and animals being slowly tortured to death for sport.
The Jewish people did have a code of concern for the poor among them such as the more wealthy were commanded to allow the poor to glean what they could find from the fields, but among the Pagans charity was neither encouraged nor widely practiced. A fairly common theme reading through philosophical writings of that era shows the general consensus that mercy and pity were defects of character and not traits of rational people.
Pliny the Younger wrote his concern that charities that gave to the poor should probably not even exist. Even Plato said that a poor man who was no longer able to work because of sickness should be left to die. Plautus wrote: "you do a beggar bad service by giving him food and drink; you lose what you give and prolong his life for misery."
And Christianity, despite its own bad acts, changed all that--changed the culture. For the first time, active concern and ministry to the poor became not only socially acceptable, but exemplary. Compassion as a human emotion, and unrelated to currying favor or self-benefit, became a standard human trait for perhaps the first time in history.
And now I believe Americans from the most dogmatic Atheist to the most devout Christian believer shares pretty much the same sense of right and wrong because of the Christian influence over the centuries.
What I always find interesting is reading ancient pagan accounts of Christian rituals. Their misunderstanding of Christians concepts delves into the realm of absurd. One of my favorites can be found in the
Octavius of Minucius Felix (link provided below) wherein the author refers to a letter written by an early 1st century CE teacher of Marcus Aurelius, named Marcus Cornelius Fronto. In chapter nine, Fronto describes that Christians only meet in secret late at night and identify each other with secret symbols and marks. They consider themselves all to be brothers and sisters and refer to each other that way. He then goes on to describe drunken incestuous orgies (if they accept themselves as brother and sister and engage in lustful activities it is incestuous). He describes an initiation ritual where a baby is covered in flour and beaten to death. The followers then drink the blood and eat its flesh and praise God in the process. They tempt a dog to overturn lamps extinguishing all light, and in the darkness they are free to engage in lustful activities without being held accountable since no one can see.
It's a great depiction because it really shows that Christians had one hell of an image problem in the first few centuries after Christ's death. Now of course, they met in secret because they were being persecuted. At times, not always, being Christian was a good way to get dead. So no shit they are going to meet in secret.

The cannibalism charges are obvious misunderstandings of the Eucharist. Not sure where the charges of orgies come from, but many other pagan commentaries describe their shock that Christians kiss each other freely, even when they call themselves brother and sister or have just met for the first time, so it may have been an exaggeration of that.
Regardless, it's an interesting read that can really put some things into context as far as how Christians were viewed in antiquity.
Octavius of Minucius Felix Roberts-Donaldson
This version (below) is a bit more friendly as far as language, but not quite as faithful to the text, I think:
Full text of The Octavius of Minucius Felix