Lying for a good cause is still lying. But sometimes it's necessary, as the Vulcans know quite well.
I take exception to the use of the word "duplicitous" to caracterize Spock's actions in that episode; "duplicitous" implies an evil agenda. It's ironic that people stigmatizing Vulcans about their alleged lack of honesty can't do so without resorting to that kind of bastardization of the language.
Not sure anyone is trying to bad-mouth Vulcans here. Just pointing out that they're complicated and occasionally contradictory, just like any other species. They have their virtues and their flaws. They can be heroes or villains or morally ambiguous.
Which, to my mind, makes them all the more fascinating--and believable.
And "duplicitous" is not necessarily a bad thing. Secret agents are duplicitous. Kirk can be be duplicitous. (Remember "corbomite" or "fizzbin.") Outwitting and misleading your adversaries can be admirable sometimes.
Heck, that was the whole premise of Mission: Impossible. (Also produced by Desilu.)![]()
I can only take the old Mission:Impossible in small doses, after a while the whole routine becomes boring as hell, unlike ST for example that I can't get enough of. I also like the invaders, danger man, the prisoner (which is a continuation of the former), the avengers (John steed et al), plus about a dozen of others.