I've heard this argument before, and it has a point. At the same time, I wouldn't want my kid to think they can't trust me. I certainly stopped trusting adults who blatantly lied to me as a child. Best case scenario, I'd figure they're unreliable and not worth listening to. Worst case scenario, I'd resent them and it would color my behavior towards them. I wasn't always peaceful.

In the end, I think it varies kid-to-kid and by context. I can see the value in lying in order to teach a kid to be skeptical, like by stating something clearly illogical so as to make them question it. I can also see the value in "little white lies" that help protect kids or keep them from age-inappropriate information. I can see some kids adapting well and catching on to what you're trying to teach. I can also see kids that expect honesty, feeling extremely hurt when they realize someone they trust has been dishonest. I can even see it being a traumatizing event.

I'd hope that anyone who makes the decision to lie to kids will keep all that in mind. Unfortunately, I imagine more people using this excuse the same way the uncle who threw you into a pool said they're "teaching you how to swim." It can easily just be a way to do something awful, and I doubt most people have the tact or follow-through to ensure a lesson is actually taught.

Just some food for thought.