Lying is theft. When you tell me something which I take to be true and as a result I invest my time, or my money, or even my care, you have stolen these things from me because you obtained them with false information.
Lying creates inequality. Since you also do not like being lied to--I have never known anyone who wanted to be deceived-- you have acted as if there were two classes of humans: you, with the right to lie, and everyone else, who must be truthful to you so that you too will not lose your way.
Lying treats people as means to the end you wish to accomplish, and not as ends in themselves.
Lying is one of those rare areas in which the moral rulebook and the legal one overlap each other quite neatly. Fraud is defined as an intentional falsehood on which another relies to his detriment. A fraud is a lie writ large, often in a financial context, where the damage to me is quantifiable in money. Even those lies which the law does not define as fraud tend to fit the same definition: a knowing false utterance which the mark is intended to rely on to his harm, and does. The only differences are of degree, for example, when we cannot assess the loss in money.
The basic tenet that lying is wrong seems to be universal to all cultures, probably because humans are social animals. To live together in a society we must tell the truth to each other about such basic matters as sources of food or of danger. Sissela Bok writes in Lying: Moral Choice in Public and Private Life:
A society, then, whose members were unable to distinguish truthful messages from deceptive ones, would collapse. But even before such a general collapse, individual choice and survival would be imperilled. The search for food and shelter could depend on no expectations from others. A warning that a well was poisoned or a plea for help in an accident would come to be ignored unless independent confirmation could be found.
Since even liars agree that lying is wrong, to the extent that they do not wish to be lied to and to lose their way, there are some remarkable special cases in our society: we justify some lies and are resigned to others. Why does indignation fail in certain cases?
Public and private spheres. Before looking at specific cases, I would like to dispose of the idea that, where lying is concerned, there is an important distinction to be made between public and private life. Some people believe lying is more justified in one area than the other. This can cut either way: we tolerate a politician who lies because he adores, and is rigorously faithful to, his wife of forty years. Or we excuse a friend's marital infidelity because we believe him to be of complete integrity in business relationships.
Ross Perot pointed out, correctly in my view, that where lying is concerned you cannot separate the spheres. He did not want adulterers working for him because "any man who will lie to his wife will lie to me." You can test this assertion by asking yourself: why wouldn't he? Because his wife is a thing to him but I am a person? There is no answer to the question likely to inspire continuing confidence in the individual. Once we know that another violated a relationship of trust and reliance, there is no moral distinction to be drawn based on the "sphere" in which the deed occurred.
Infidelity. Sexual infidelity has become so common in our society that it is increasingly treated as if it were a sociological phenomenon rather than a moral issue: men are more likely to have multiple mates and families during life, women are more...