The sense of an absolute moral orientation is weakest at the extremes of wealth and income in any society, amongst the richest because they can deploy resources to evade the consequences of any transgression, and amongst the poor because they have little or nothing to lose and much to gain. The strongest sense of moral rectitude, the strongest belief in moral absolutes, is felt by those in the middle of the distribution, since those towards the centre are threatened not only by those at the amoral extremes but also by competition from those immediately above and below them. The middle of the distribution benefits most from moral regulation, and loses least.
But away with crude binning, and the class analysis that it implies. Take any three individuals and arrange them in order of wealth, and the chances are that the central individual will have the strongest sense of objective morality. Put a society's individuals in order of wealth, or arrange them in order of income, or some combination of both, and, in spite of numerous exceptions, it will be found that proximity to the centre of the range is an excellent predictor of the strength of absolute moral adhesions.