It never actually states they only have sex once every seven years, merely that there is a necessity to do it then. Doubtless the rest of the tie they dabble
Absolutely not. Vulcans repress and control strong feelings and urges. Sexual urges can be the strongest and most disruptive, a prime area for them to concentrate on with their disciplines.
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There was a
point to the idea of Pon Farr. It wasn't some random plot element dropped in for no reason. The point of it was to explore how the race can continue, what with these rigorous disciplines against all urges and feelings.
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Expect the makers of ST to have a thoughtful purpose behind what they do. Theodore Sturgeon was a novelist with depth to his work. (My 2nd favorite novel ever, his "More Than Human".)
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It's not that they "can't". It's that they
don't. But they "don't" so much, that it's become part of their biology, so there's a bit of "can't". This biological imperative has been squelched by a combination of discipline, culture, and biology. Biological imperatives have a way of confounding all controls in the end, though, so somehow Pon Farr arose as a safety valve, allowing the race to continue.
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(Remember, Spock explained to Kirk that it was about reproduction, and if they were doing it apart from Pon Farr, reproduction would not be an issue. That would be covered, all that sex would mean that wasn't any problem. Pon Farr ensures reproduction, which would not be under threat for the species if routine sex were going on.)
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We were really meant to get it , in no uncertain terms, when seeing and hearing Mr. Spock, that such a guy does not have sex. Just hearing about Vulcan disciplines should drive that home, but it's a thing you have to stop and think about. The Vulcan disciplines were not about just not telling jokes or laughing, or tearing up at a sad movie. They're about the heavyweight urges, the ones that disrupt lives, trigger violence, and supply the sublimated energy for all sorts of insane causes.
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So sex doesn't have to lead to all that? Argue with the Vulcans, it's not my ideology... though I can very much see their side on this. Historically sex is great big powder keg.