This is long and off-topic, but the above post warrants a serious reply.
I don't insist on the truth from my kids because of some disembodied principle; I demand it because it's an integral part of my authority. I'm not with my kids all the time now, and the older they get the less I'll be with them and the easier it'll be for them to get away with telling me whatever the hell they think I want to hear. Since I operate under the realistic assumption that all kids will at some point be up to some stuff that they don't want their parents to know about, I've started beating it into them at an early age that you don't lie to your parents. I don't do this because I'm particularly authoritarian: I'm a pretty relaxed dad with a couple of great kids (so far, at least), and I don't have to have many rules. I do it because the teenage years are coming, and you have to operate under the assumption that all teenagers are reckless idiots with a death wish, and I think in order to help them navigate through that, you have to be able to occasionally put on the I AM DAD, MASTER OF THE UNIVERSE hat. And that frankly has to be based on a kernel of fear. You don't openly defy me or lie to my face, or I will kick your ass.
I think we all knew kids growing up who would happily and easily lie to their parents all the time, and the parents would nod genially and obliviously and believe it all, and then the kids would head out to recklessly do exactly what they just promised that they wouldn't. I'm not going to be that parent. If my kids are going to lie to me, they're at least going to squirm about it like I did when I lied to my parents. I was so thoroughly conditioned to hate and fear lying to my folks that it was a real deterrent sometimes.
I don't see how you can have any authority if your kids learn that lying to you is no big deal. And if you don't have any authority, then pretty much all you can do between puberty and college graduation is watch from the sidelines, wring your hands, and hope things turn out. Maybe you think it's "selfish" and "more about [me] than the liar," but mostly I am concerned with seeing the liar live to adulthood.