It seems to me patently obvious that we can no more respect and tolerate vast differences in notions of human well-being than we can respect or tolerate vast differences in the notions about how disease spreads, or in the safety standards of buildings and airplanes.

Harris is arguing against a strong form of moral relativism. He suggests that disagreements about “human well-being” are not merely cultural preferences but can be evaluated with something like the objectivity we apply to medicine or engineering. Just as we do not treat every theory of contagion or every building code as equally acceptable, he claims we need not treat every moral system as equally worthy of respect when the stakes are human flourishing and suffering. The analogy implies that moral claims can be constrained by facts about minds, bodies, and societies, and that some “notions of well-being” are demonstrably harmful in ways that justify criticism rather than tolerance.