"Lying is unhealthy for one's life"

I hate being lied to. Short of violence, it is the worst thing you can do to me. Not because of God, or the Ten Commandments, or any universal moral precepts. The reason that I hate lies is because, like you, I wish to navigate carefully through life, and to do so I must be able to calculate my true position. When you lie to me, you know your position but you have given me false data which obscures mine.

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.