I think Steve has provided a very helpful guideline for us to decide when lying is bad and when it is "pro-cooperation". Some people can laugh it off when you tell them the truth while others take it badly, and we need to apply our wisdom and decide how and what we say affects others. I vaguely remember reading your comments on other social issues, and I must say you are very insightful, and your message is crystal clear. Thank you.

People's happiness (and quality of life) depends on the smooth running of society, abundant food, safety, things like that. All of these things depend on consideration for others, and cooperation. So any action that promotes cooperation is good and any action that obstructs cooperation is bad. Looked at like this, it's extremely easy to tell whether any behavior is good or bad. There's no need for debate nor excuses; it's very simple. "Knowingly providing false information in order to gain a personal advantage over another person or group" is a good definition of "lying", and that behavior is obviously going to obstruct social cooperation (since it favors the good of the self over the good of society). There are cases where not telling the "whole truth" is pro-cooperation. E.g. I think my friend's shirt looks very silly but I refrain from mentioning it since no good can come of it. That case obviously does not fit the definition of lying that I gave. But giving misinformation about my feelings if I'm asked is only lying if it benefits only me. So you need to think about your motives, and the consequences, each time you consider not telling the truth, to see whether or not the result will be a lie. It's common to see "telling the whole truth" as universally good and anything other than that as universally bad, but I think there's a more helpful way of looking at it (which I've tried to explain here). :D Sorry that this is not a correction, but in this case I felt that the concepts needed more attention than the language (which is very good).