Completely alien? No, there is some vague sense and memory of divine image in every man. But alien in parctical sense, YES.
Now, to demonstrate it to you, no complex reasoning is need, but only simple facts generally known. Have a look at the societies like pagan Rome or Greece. In Greece it was considered a virtue to kill handicapped children. In pagan Rome the intelectual, moral, political and spritual elite was enjoying the circus where slaves were killed in ingenious and various ways to give pleasure and esthetic satisfactions. The general population and elite was enjoying this spectacle publicaly without any scruples.
This innocent enjoyment was spoiled later by "narrow minded" Christians, who brought the new awarness or gentle light of Gospel. It is true that the enjoyment of cruelty remained and pagan vices or false virtues persisted, but they went underground, covered with shame and hypocrisy.
Or see the example of Aztecs who saw it a virtue to practice their rituals (BTW the reason why few Spaniards so easily defeated a large Aztec empire, was that subjected Indian tribes preferred them over previous rulers).
Pre-Judaic cultures were well aware that lying, cheating, stealing, not keeping one's word, etc. ..were WRONG, and they didn't need a formal, monotheistic religion to confirm this for them.
Hmm, not really, in many cultures robbing and deceiving the strangers was seen as a good thing.
And in today's world, atheists are no more or less likely to act unethically than people who are formal members of a religion.
Well, let us not be blind to the facts. The first atheist state - Soviet Union falsified your claim. The first neo-pagan, post-Christian state Germany also was very revealing.
The first atheist state - Soviet Union falsified your claim.
But it doesn't falsify it at all. He allowed how as atheists are no more or less likely to act unethically -- therefore evidence of unethical actions in a antheist is is not proof that atheists are more unethical -- just as the Spanish Inquistion shows that Christians are capable of mass murder, does not mean Christians are all mass murderers.