Nietzsche once wrote something to the effect that the Christian Church was responsible both for the creation of the problem of sin and for the means of its alleviation. By this, he was speaking largely of the psychological sense of guilt and shame felt by the "sinner", instilled in them as a result of years of church indoctrination, which could then be alleviated by asking forgiveness of the Christian God (primarily employing the Church Priest as a necessary intermediary). Nietzsche felt that this imparted sense of guilt was a problem for humanity's potential. Guilt and shame may be natural human responses to ones causing large-scale destruction and disorder (though even here, this position seemed debatable to Nietzsche) but had little place when applied to the petty sins of the average person. The Christians seemed, so suggested Nietzsche, largely unconcerned with sins of murder and rape and abandon because such were (and are) proportionately rare and may be policed by other means (the powers of the state generally taking a direct interest in such things). Instead, the Church largely seemed concerned with torturing its adherents with threats of fire and brimstone for gaffs such as gossip, gluttony, pettiness, spite, envy, and illicit sexual expression. These, Nietzsche mused, far from being reasons for censure, merely represented the natural outpouring of human expression. In other words to sin, or to transgress perceived moral order in petty ways, represented no more than the natural grist of human social interaction. To attempt to police or control such natural expressions was not only wrong but censured a vital aspect of human creativity. Nietzsche believed that the psychological stranglehold of sin was too powerfully entrenched in his society to be overcome all at once, but he suggested that the necessary framework for sin's disintegration had already been laid via what he termed the death of God--whereby the psychology of belief would slowly vanish and the age of the Christian God would be at an end.
If the above "myth" seems reasonable to you, it shows just how far Nietzsche's thought has taken hold. Nietzsche is often credited as a prophet of late modernity and, I would suggest, his prophecy concerning the alleviation of the wide-spread psychology of a sense of sin has proved more or less correct. This is not a particularly controversial claim. I would also suggest that Nietzsche is correct, at least in part, in suggesting that a sense of guilt and shame for a person's perceived transgressions of the moral order are not entirely "natural" but are themselves learned responses. This is also not particularly controversial, though there is much room to quibble at the extremes as to what and whether there are behaviors that would engender such responses even without education concerning a perceived "moral order" (for, we are all mortal men doomed to die, which speaks to a fundamental ontology). Leaving aside the rather large metaphysical question of whether there is or is not an actual God in the heavens to begin with, there is a distinct dividing line in thought as to whether or not there is any use in passing censure concerning what was traditionally referred to as the "moral order". Modernity seems inclined, alongside Nietzsche, to view the development of this concept of sin along anthropological and political lines, seeing in this idea the means by which the old social order maintained control of the populace. For, so long as people remained convinced that they were beholden to an entrenched authority lest they face eternal damnation, they were little disposed to question the wisdom of their leader's policies concerning the promotion of the general welfare. So long as the ruling class supplied them with priests and the means of expiation and salvation, what more could they really ask for? Alleviate this petty psychological prison, spake Nietzsche, and you would unleash the pent up human potential which had been suppressed for the last two thousand years. There is undeniably some truth to this myth of power, for there is no question that this sense of sin creates a power dynamic that can be exploited.
But the other side suggests a myth which, if somewhat darker, is equally compelling. Its myth begins with a perception that there is something very wrong with the world because there is so much death, disease, hatred, violence, and the like. Nietzsche (who whatever else he was was personally no reveler in depravities of violence) would not disagree with this assessment but he seems (alongside the resulting modern intellect) to draw a dividing line between such horrible, bad, and cruel behaviors and suggests that the ordinary person (since, for Nietzsche, the ordinary person is ever and always basically no better than a slave) is too petty and trivial to need to worry too much about getting to that point. The only ones capable of such "sins" are the "great" human beings, who, because of their strength and grandeur truly understand that they are better than everyone else and, so long as they are acting out of grandeur, for whom such cruelty might be justified (and, regardless, who is to tell them that it isn't?). This isn't really a problem for humanity, because such "great" souls will always be very few in number. The Christian myth, however, (for we are talking about Christianity here) suggests that there is no ontological divide between two types of humans, the slave and the high, and that so much of what constrains human vice is not desire but opportunity. Those sins that appear to Nietzsche petty and beneath notice, are only petty because most persons, by the grace of God, are constrained by circumstances to a somewhat more moderated expression of their sinfulness. If given opportunity, most would likely fall into the same "grand" vices of the great, because that is what their hearts so desire. The smallest of sins are important, so reasons the Christian, because the disordered desire at the heart of the small sin which hurts few is the same as the disordered desire at the heart of the great sin which hurts many. If you want to teach a person how to prevent harm to their fellows, you can't start with the "great" sinner who is already powerful and far gone midst his roiling passions, but must teach the "meek" how to moderate their small passions. For, (and here is the great Truth of Christianity which Nietzsche and all such aristocratic thinkers attempt to overturn) there are no "great" souls and "small or slave" souls. Humanity is not ontologically divided into castes, but is democratic in that all human persons, no matter how high or low they appear, are icons of God himself, having been created in his image. Being an icon of God, all human action reflects a grandeur, even if perverted by sin, which may result in the destruction of the world if allowed to blossom.
But this is a truth too terrible for Nietzsche (or for modern man) to contemplate. For, if in the heart of every man, woman, and child beats an appetite so great as to consume the whole world, what hope is there? If all persons are a potential Mao, or Stalin, or Hitler, then what hope is there for humanity? Weep, oh modernity, weep and despair, for your concept of evil is too small, too small to compass the darkness nipping at the outing reaches of your blackened souls, blackened so darkly that they are unable to perceive their own darkness. Weep and despair, for such despair is the only hope of your redemption!