Harris, third paragraph:
A rational approach to ethics becomes possible once we realize that questions of right and wrong are really questions about the happiness and suffering of sentient creatures.
I agree that ethical questions eventually reduce to happiness and suffering. I doubt, however, that this understanding makes possible a "rational approach to ethics," if by "rational" Harris means that ethical statements can be judged as true or false.
If we are in a position to affect the happiness or suffering of others, we have ethical responsibilities toward them—and many of these responsibilities are so grave as to become matters of civil and criminal law.
I suspect that Harris again wants to equate the naturalistic and ethical meanings of a concept, in this case, the concept of responsibility. We can speak of any natural causes as those activities that are responsible for their effects. For example, gravity is responsible for keeping planets in orbit around the sun. But to have an ethical responsibility is not merely to be the cause of someone's happiness or suffering. I would argue that ethical responsibility exists only when someone cares about another's happiness and suffering and feels a sense of obligation or duty to promote the other's happiness and avoid causing suffering. Harris seems to suggest that the duty is there, whether or not someone feels a sense of obligation. He speaks of "grave responsibilities" that exist prior to being encoded into human-made laws. But this is another example of confusing moral rules, which are contingent on people, with natural laws, which existed before people came into existence.
Taking happiness and suffering as our starting point, we can see that much of what people worry about under the guise of morality has nothing to do with the subject. It is time we realized that crimes without victims are like debts without creditors. They do not even exist. Any person who lies awake at night worrying about the private pleasures of other consenting adults has more than just too much time on his hands; he has some unjustifiable beliefs about the nature of right and wrong.
Like Harris, I am totally opposed to the criminalization of all acts between consenting adults. Unlike Harris, my argument is based on my dislike of people meddling in others' private affairs, not on an argument that the meddler's beliefs are rationally unjustified. Knowing that a lot of people are fornicating causes the meddler unhappiness and suffering. He would feel much better if the fornicating stopped. So, it is his happiness (and the happiness of like-minded moralists) versus the happiness of fornicators. Whose happiness is more important? Harris would have us think that this question has a rational answer, as if some pre-existing natural-law-like principles for resolving conflicts of interest could be discovered by investigation, just as natural laws can be discovered. But no such principles of fairness and justice exist. Human beings have invented them out of the need to resolve disputes. Invented, not discovered.
Harris, fourth paragraph, p. 171:
The fact that people of different times and cultures disagree about ethical questions should not trouble us. It suggests nothing at all about the status of moral truth. [Harris draws an analogy to ancient humans having differing (and incorrect) views of natural phenomena such as fire and the stars because they lacked the tools to discover truths about natural phenomena.] Their lack of consensus signified their ignorance of certain physical truths, not that no such truths exist.
If there are right and wrong answers to ethical questions, these answers will be best sought in the living present. Whether our search takes us to a secluded cave or to a modern laboratory makes no difference. If ethics represents a genuine sphere of knowledge, it represents a sphere of potential progress (and regress).
The analogy to truths in physics is misleading because it is only an analogy. Moral rules are not natural laws. Ethics are based on feelings, desires, and motives, which are neither true nor false. Ethics is not a sphere of knowledge that can become more accurate. The reason that people differ—not just across times and cultures but within a culture at one point in time—in their ethical views is that they have different feelings about activities. Activities that make some people happy can thoroughly disgust others. Trying to objectify the feelings of one group of people as more correct than another is a category mistake, like trying to say that sounds possess color. Feelings do not possess correctness or veridicality. Of course the hope is to convince others that one's preferred moral principles are objective because, if accepted, it would give one more leverage in an argument about how to behave. But the argument always reduces to whether people feel happy or unhappy about activities, and those feelings differ across individuals.