I always thought this was a bullshit cop-out.

No you didn't, you lied.

s1e9 "Prime Factors"

Sometimes lying is the most logical course of action.

I think they technically say that Vulcans don't lie, not that Vulcans can't lie. That would imply that they prefer to avoid it, but can if they need to. I mean, if Tuvok couldn't lie then he never would have been able to go under cover as a member of the Maquis.

Londo: I do not lie when I say this could have been a major embarrassment to all concerned.

Sheridan: Oh, I'm sure ambassador. You don't lie, the Minbari don't lie, no one around here...

Londo: Who said the Minbari don't lie?

Lying is practically all the Vulcans do according to Enterprise.

All Vulcans know how to do is be bisexual, eat hot chip, and lie.

I don't understand why people assume Vulcans and Data can't lie because they don't have emotions.

You don't need feelings to lie.

It's known on earth as politics

Where you bend the truth, modify explanations, omit certain facts, exclude details, interpret data, make your own calculations or highlight known unknowns as well as unknown ones. Then you talk in great detail about everything without ever passing along any new information ... it's a highly developed skill.

But in everything you do ... you never lie, you never tell an untruth .... you just use logic and reason and stating certain truths while omitting others to make the other person believe what you want them to believe.

Also true for Minbari.