Lying by itself is unequivocally a bad thing, in my view. My goal in life is to learn as much as I can about Reality and The Universe. Anything that detracts from that goal is a negative action, in my view. Obviously, other people have different priorities.
The rule is absolute, but its effects are not. Consider the SS/Anne Frank scenario brought up earlier:
|Lying|<|assisting Hitler in the Holocaust|
Therefore,
(Saving Anne Frank)+(Lying)= a net good,
even though lying by itself is bad.
The reason they don’t teach this moral calculus in math class is precisely because it is so imprecise and inconsistent. For some small few, the benefits of saving Anne Frank do not outweigh the detriments of lying.
A much larger number might argue that the negative aspects of lying outweigh the positive aspects of, among other things, boosting self esteem or letting a competitor’s inferior idea prevail. I am one of those. And since I define lying as ‘obscuring truth, or withholding information in order to influence one to make choices one wouldn’t have if one had all relevant information,’ I consider most advertisers and politicians professional liars.
Anyway, the answer to the thread title is “when the beneficial effects of lying outweigh its inherent negative effects.” Which isn’t helpful, because people like me will place lying extremely low on the high-is-good-low-is-bad scale, while people like GW Bush will place lying into neutral or even inherently good territory.
Legally, lying should be almost always allowed, because the benefits of much more freedom outweigh the benefits of a little more truth. Morally, you can say lying to your wife to make her feel prettier is okay, while I can despise politicians and advertisers to my heart’s content.