Humans are endowed with a wide array of moral capabilities. These are the essential social glues - the capacity for altruism, loyalty, sacrifice, justice, fairness and guilt - that culminate into a conscience that motivates people to behave ethically so that there is peace, social stability and that life can go on with as little trouble and as much happiness as possible.
But at the same time as humans are capable of morality, humans are also brutally capable of moral flexibility, switching morality on and off in order to maintain self-interest in the struggle for survival. Equally, humans are often ignorant of their propensity for moral flexibility other than the oft-felt nuance that edges them towards thinking for oneself in the form of temptation.
As Robert Wright writes in The Moral Animal, "human beings are a species splendid in their array of moral equipment, tragic in their propensity to misuse it, and pathetic in their constitutional ignorance of the misuse."