It's easy to be concerned that, whichever answer this question gets, that will somehow serve to undermine morality itself. If, on the one hand, our moral sense is one with which we're born, then it's, in effect, genetic, and our gut reaction to human suffering can be written off as a consequence of the evolutionary value of protecting the herd. But if, on the other hand, our moral sense is a product of our environment, then it looks wholly non-objective: Jones, who grew up in a wealthy New York family, might have a completely different moral sense than does Wang, who grew up in poverty in central China, and there's nothing to choose between them. It's just a matter of their different environments. What's really distressing, frankly, is that one actually hears this kind of concern expressed by the otherwise intelligent scientists---psychologists, mostly---who are working on this very question. But the danger isn't real. The sense that there is a danger here is due to a failure to distinguish our ...

I'm not sure why one would suppose that "love of others"---by which you seem, obviously, to mean romantic love---is a "supreme value", expressing which over-rides so much else. That said, yes, this kind of question is very real. And surely it's possible for someone to decide, in certain circumstances, that it is better to have an affair than to destroy a marriage, neither option being a very good one.

Sorry, but this is a silly argument. Replace "animal" with "person", and you get an argument in favor of breeding children for slaughter. ( Apologies to Jonathan Swift .) But yet, surely, it's better for a person to exist than for it not to exist, right? Actually, that's not so obvious, as we'll shortly see. But if it's not obvious in the case of people, it's certainly not obvious in the case of animals. The argument purports to show that it's (objectively) better for an animal to exist than for it not to exist by showing that, if it were (objectively) better for it not to exist, then we ought to sterilize all the cows. But this assumes that, if it's not (objectively) better for an animal to exist than for it not to exist, then it must be (objectively) better for it not to exist. But the obvious reply is that there's just no better or worse about it. It's neither (objectively) better for one more cow to exist nor (objectively) worse. But then the argument goes nowhere. What's fundamentally...

Here's a simple-minded answer to this question, but I'm not sure that doesn't mean it's right. Consider the question whether women should have rights equal to men's. Two centuries ago, this would not widely have been accepted, whereas nowadays it is, at least in Western cultures. So what reason do we have to believe that our understanding of this particular moral question is better than that of our ancestors? That seems just to be the question what reason I have to think I'm right and they were wrong. But that, in turn, just seems to be the question what reason I have to believe that women should have rights equal to men's, and I take myself to have plenty of reason to believe that. I think if you asked what reason we have to believe that our understanding of the nature of the physical world is better now than it was 200 years ago, I'd have to give pretty much the same answer.

I think the really deep question here is why incestuous relationships seem so morally problematic, quite independently of the child-bearing issues. Here are a couple thoughts. The case of parent-child incest is clearly the most problematic, even when the child is of age. And here, I think the source of concern is power. It's not that it seems utterly impossible for the child, in such cases, to give truly informed consent, but one might wonder how free (or well informed) that consent could be. It's not unlike, that is to say, supervisor-employee or teacher-student relationships, except, of course, that the parent-child relationship is far more intimate and, as a result, far more is at stake for the child. What, then, about sibling-sibling relationships? Here, there probably aren't the same kinds of concerns as with parent-child relationships. But, continuing the work-world analogy, it is perhaps worth noting that many companies bar relationships between co-workers as well as between supervisors and...

The laws concerning statutory rape—laws that make it a crime for anyone to have sex with a person under a certain age—are justified by the belief that people under a certain age cannot give informed consent to sex. It seems reasonable to suppose that this is true, though the age in question might be a matter of debate and, in fact, the laws in different countries, and even in different US states, set different ages. So one might regard it as silly that the law in some particular jurisdiction regards a 17-year-old as incapable of informed consent, and I'd agree with you. But it's not at all obvious what the age-limit ought to be. That said, however, it is important to note that it is not the relative ages of the parties to the act that are relevant but their absolute ages. The reason "society" sees nothing worthy of legal intervention in a sexual relationship between a 60-year-old and an 18-year-old is that it regards the 18-year-old as capable of informed consent.

I have encountered this argument before, but I don't really understand it. In short, it seems to go: We are part of nature, so nothing we do can be counted unnatural. So far as I can see, that is a simple fallacy based upon no more than word play (or, perhaps, a confusion between purely descriptive and broadly prescriptive senses of the term "natural"). The kinds of freaky creatures that now populate the landscape around Chernobyl are part of nature, too, but that does not make them "natural". Unlike locusts, human beings can choose what they do to the Earth. They ought to choose wisely. Perhaps you do not share the sentiment, but many people believe that we ought not needlessly drive pandas to extinction not because it is nice for us that there are pandas around but simply because it is a good thing, period, that there are pandas around. This attitude involves a certain kind of resepct for nature that is, it seems to me, difficult to explain and more difficult still to justify. But...

I'm not so sure I agree with your initial premise. Suppose the trait in question is having red hair. It seems rather irrational of you to dislike people who have red hair, and for that reason there does seem to be something morally suspect about your attitude toward people with red hair. It seems, in particular, very unlikely indeed that your reason for disliking such people is just that they have red hair. It seems much more likely that your reason is that you think people with red hair are all whatever, and you (quite reasonably) dislike people who are whatever. It's the generalization, then, that is objectionable, because it is unfounded. And if we now consider the cases you mention—weight, physical or mental disability, or race—it seems all the more likely that it isn't just the mentioned quality that people dislike: They think people with the mentioned quality have some other sort of failing. More importantly, however, the kind of discrimation suffered by the kinds of groups you mention...

It is crucial, I think, to recognize that the relevant question here is not: Are the lives of humans more valuable than the lives of (other) animals? The objection to killing animals need not presuppose that animals' lives and humans' lives are of equal value. Most defenders of animal rights would not, I think, hold such a view. Their claim, rather, is that animals' lives are of sufficiently great value that they ought not to be killed. Note that saying that animals ought not to be killed does not imply that it is never morally permissible to kill an animal. Humans ought not to be killed, but most people would hold that it is sometimes morally permissible to kill human beings, for example, in self-defense. If (say) cows lives are of less value than are the lives of humans, then there may be circumstances in which it is permissible to kill a cow but in which it would not be permissible to kill a human being. But it does not follow from that fact that it is permissible to kill a cow just...

It seems to me that it is sufficient if there is a description of the act under which both parties consent to it. (I find myself tempted to say: ...and under which they both perform it. That may not be necessary but probably is.) Whether there are other descriptions under which one or another of the two parties has not consented to it seems irrelevant (especially if it is not a description under which they perform it): It will always be possible to find such descriptions. (Note that this is different from saying that there are descriptions under which one of the parties would withhold consent. Whether the existence of such descriptions would be relevant is a more difficult question.) If so, then the fact that X and Y, in the first example, happen to think of the consequences of their encounter in different terms does not seem to undermine their consenting to: having a sexual encounter. (And that, of course, is a description under which both of them perform the act.) There are undoubtedly...