I think that claim is vastly overblown. Have you read The Ten Commandments lately? Several of them are about appeasing a jealous god or about behavior that is difficult to think about in terms of morality, like a prohibition on swearing oaths.
The prohibition of murder did not arise with the ten commandments, with Judaism, or with Christianity. Every society contemporary to those of Christianity's founding viewed murder as immoral. Most of them had no idea the Ten Commandments existed, and certainly didn't need them to understand morality.
Greek philosophers had been discussing and debating the nuances of morality for centuries before they were exposed to Jewish writings through Christianity.
To suppose they took their ideas about morality from the Ten Commandments is, and please don't take offense, absurd. That is not what happened. Greek and Roman philosophy about morality was far more complex and nuanced than the Ten Commandments, which are by comparison crude and thoughtless.
In actual practice, the Christian church as it grew in Europe and exercised power was not a force for moral good. The church partnered with the powerful to grow its wealth and influence, and in the process grievously hurt people without power. That is of course the opposite of morality.
I can't think of any organization with less sense of morality than the Catholic Church in the past century. The atrocities they committed in Ireland and Canada alone are enough to demonstrate that they have no idea what morality is, without even getting into the child sex abuse scandal.
Who are the most immoral people in the United States today? Obviously, Evangelical Christians are. All you have to do is watch them slathering to persecute people who are different from them to understand that, to watch them cheer for Trump and other horribly immoral people like him.
Nothing in the Ten Commandments serves to stop them from being among the most horrible people on earth. Because the Ten Commandments aren't about morality.
The commandments are about a jealous god, and the world would be far better off without the systems of thought that grew up around their crude dictates.
