From p. 7 of Man for Himself: An Inquiry into the Psychology of Ethics
I have written this book with the intention of reaffirming the validity of humanistic ethics, to show that our knowledge of human nature does not lead to ethical relativism but, on the contrary, to the conviction that the sources of norms for ethical conduct are to be found in man's nature itself; that moral norms are based upon man's inherent qualities, and that their violation results in mental and emotional disintegration. I shall attempt to show that the character structure of the mature and integrated personality, the productive character, constitutes the source and the basis of 'virtue' and that 'vice', in the last analysis, is indifference to one's own self and self-mutilation. Not self-renunciation nor selfishness but self-love, not the negation of the individual but the affirmation of his truly human self, are the supreme values of humanistic ethics. If man is to have confidence in values, he must know himself and the capacity of his nature for goodness and productiveness.
None of this is to imply that the basis for moral norms shouldn't be subject to vigorous debate; on the contrary, Fromm's basing humanistic ethics on rational knowledge requires such investigation and discussion. And over the next several months I'll challenge several fundamental aspects of his vision of human nature and needs. But I wanted to pause for a moment to appreciate the value of his project to ethics, politics, psychology, and human (and potentially nonhuman) well-being.