Most people accept the concept of objective truth. If someone says that ice cream is a health food, that person is simply wrong. But if someone says, "ice cream is delicious," that statement is neither true nor false; it is simply a matter of opinion. A lot of people today place morality in the latter category. I hear this all the time: "Morality is subjective," they say. As Bertrand Russell asserts, "in a question as to whether this or that is ultimately Good, there is no evidence either way; each disputant can only appeal to his own emotions, and employ such rhetorical devices as shall rouse similar emotions in others." I disagree. Although people's emotions do often influence their views on morality (or, for that matter, on any other subject), it is possible to objectively assess a moral view based on the quality of the reasoning used to support it and on the weight of the evidence.
All societies share certain core principles. Killing would be a crime even in Hitler's ideal society. What Hitler claimed was not that killing in general was acceptable, but that the only way to create an ideal society was by first destroying or enslaving certain races. That claim rested on demonstrably false assumptions about reality, such as his pseudoscientific notions about race and the mortal threat that Jews allegedly posed for the rest of mankind.
Morality and truth are more closely linked than subjectivists admit. According to the subjectivist, if one culture practices cannibalism, and a second culture considers cannibalism immoral, there's no objective way of determining which side is right. If we investigate how the cannibals justify their actions, however, we are likely to find that they hold mistaken beliefs. They may believe, for example, that eating human flesh gives a person great powers, or that the people they are eating are less than human, coming as they do from outside the tribe. To suggest that those beliefs are rooted in superstition and ignorance is hardly a matter of subjective opinion.
By identifying core beliefs that all societies accept, we can determine through reason which moral views come closer to meeting those core beliefs. We can also determine when moral laws have exceptions, such as killing in self-defense. Since the goal of the law against killing is to protect human life, occasionally we must violate this law to reach the same goal. The reasoning here is similar to why people undergo surgery: they allow their body to be damaged in the short run to improve their health in the long run.
Moral ambiguity arises from the conflict between short-term and long-term consequences. If the United States government had learned that hijacked planes were heading toward the World Trade Center, it may have chosen to shoot down the planes, killing all the passengers, because failing to do so would lead to even more deaths. As a rule, long-term consequences take priority over short-term consequences. The problem is that they are harder to determine. The Nazi worldview perhaps represented the extreme of reasoning on the basis of long-term consequences, in the suggestion that enormous destruction of human life was needed to create a peaceful world. The primary danger of utopian visions is that people who seek to transform society to such an extent may ignore the harm they are driven to inflict on society in its current state. Sound moral reasoning involves a balance between what one knows to be true in the present and what one can reasonably infer about the future.
In real life, of course, many of the situations we face are not as clear-cut as the previous examples. The fallacy that subjectivists commit is in thinking that lack of clarity automatically implies subjectivity. Objective reality is not always accessible to human knowledge. For example, nobody knows whether life exists on other planets, but either it does or it does not; the answer does not depend on what humans believe or know. Of course, we may disagree on how to define life. But everyone agrees that humans, lions, trees, and bacteria are alive. The concept does not collapse into subjectivity simply because people aren't sure how far to extend the definition. By that logic, all concepts would turn out to be subjective.
Similarly, the fact that two people in full knowledge of the facts reach opposite conclusions on a moral question does not imply that the issue is subjective. One person may err in his reasoning, and their views may rest on assumptions that are hard to prove. Uncertainty is not subjectivity. While a person's emotions may influence where he stands on the issue, a rational person recognizes that any attempt to resolve the issue is ultimately a search for truth, not an appeal to emotions. Just as unsolved mathematical problems do not shake people's faith that one plus one equals two, complex moral issues do not refute the existence of simple moral truths.
After all, anyone who enters any moral debate hopes that this society will eventually resolve the issue when most people decide which side’s arguments are the most cogent. If neither side is ultimately right or wrong, however, then the view that triumphs in the end will do so simply because its proponents have enough political power. All moral controversies are ultimately power struggles, if one follows moral subjectivism to its logical conclusions. Only moral objectivity can offer the promise of a sound resolution.