So basically you confirm that there are plenty of things in Trek which flat-out contradict your views, but you choose to ignore them (let's forget about "The Chase", let's ignore Voyager "Blood Fever", let's ignore Trip and T'Pol having sex on ENT but we'll still remember that they couldn't conceive naturally... selective memory is a great way to argue for one's views...), and nothing to support it but your speculation and interpretation of certain lines.
Did Spock in "Amok Time" ever express the desire to have sex with any other Vulcan? Why T'Pring? If he specifically needs a Vulcan, why not look for some other Vulcan woman? The episode makes it clear that he wants to go back to T'Pring, not just to Vulcan, and it is because they were betrothed and telepathically linked (even though the latter obviously is not a absolute assurance, or T'Pring would have felt the same as Spock and would not have hooked up with Stonn). If a Vulcan feels the need to be with a mate (not that it's necessary - The Search for Spock makes it clear that, if no telepathically linked mate exists, a random person you're not telepathically linked to can work just fine), well, Sarek has his mater: is
married to Amanda, and most likely telepathically linked with her as his mate (why wouldn't he be? We know that Vulcans can mind meld with Humans, and just about everyone and everything else, establish telepathic link and transfer their feelings and thoughts and even psychophysical states to others, and vice versa).
And please, you're not going to argue that Vulcans and Humans never had sex in TOS?

What was Spock doing with Leila or Zarabeth (the latter might not have been from Earth, but looked 100% human)?
They might have went at it like rabbits. Two different species of rabbits that never had chil'rin'.
And you're not really suggesting that Amanda and Sarek have a platonic relationship that they've crowned with an artifically conceived baby?
Diane Duane did, and she's not generally considered stupid. I think it's very reasonable to state that there is a presumption--a very strong presumption rebuttable only by the clearest and most convincing evidence--that
two different species from
entirely different phylogenetic trees that diverged, even taking into account "The Chase,"
four billion years ago, should
not be able to naturally procreate. Maybe I'm just weird.
We also know that humans can have sex with Cardassians and Betazoids among others, that Klingons can have sex with Trills, that Cardassians can not only have sex with the Bajorans and the Kazon but also naturally conceive healthy children...
I'm unfamiliar with a Kazon/Cardie... some episode with Seska, I guess?
Like I said, I am willing to suspend disbelief enough to assume convergent evolution on humanoid genitals. That's problematic in itself (look at the bewildering variation on Earth!) but not self-evidently wrong. Genitals as we know them evolved in the general fashion they did for a reason, and are therefore probably a universal adaptation to a universal problem. For the same reason I have no problem with Vulcan having flying raptors or predatory teddy-bear-cat-things, I have no problem with the general notion that humanoid males have wangs of the same general type.
So why are you insisting on this, in face of so much evidence to the contrary?
Because the evidence
is contradictory, and when that happens the most reliable evidence is preferred, as is the most reasonable interpretation. I hope you're not getting upset because we don't see eye-to-eye on this issue...
If you don't like the biological rules of Star Trek, you can always try to write your own show, not try to deny what we've seen on screen.
This sort of approach will quickly reach the limits of logic--in a franchise as sprawling as Trek, there are going to be times where one thing flatly contradicts another, and you're going to have to choose which one is more reliable and move on from there.
Claiming that it doesn't make sense scientifically changes nothing - lots of things in Trek don't make sense scientifically, but they still happened in the actual shows/movies.
Sure. But that doesn't mean I ought not criticize it when they get something so disastrously wrong it ruins what came before and after--are "Threshold" and "Dear Doctor" immune from being called stupid because they have a Trek name on it? Even Brannon Braga, king of stupid, admits "Threshold" is void for its sins.
You might as well argue that Kirk never had sex with anyone ever - we never saw in on screen, right? - and that he was just a sperm donor for Carol Marcus' in vitro baby.
It would explain why Carol never told him.
Who interestingly appear to be absolutely, 100% morphologically Vulcan--for what it's worth.
What is the significance of that, even if it were true?
All speculation, to be sure. But a copper (hemocyanin?) blooded Vulcan fetus is going to be at a disadvantage in the womb of an iron (hemoglobin) blooded human.
If you want serious pettifoggery, I could point out that any copper-based respiratory pigment I know of ain't bright green. It's dark blue.
And is it even true? Yeah, Spock has pointy ears. So? Some other Vulcan/Human hybrid might get a different combination of genes and have human-like ears. The obvious outisde physical differences between the Vulcans and the Humans are too small, anyway.
A completely different biochemistry, touch- and distance-telepathy, nictitating, polarizing (?) eyelids, a remarkable immunity to radiation... same body plan, but tremendous physical differences, few if any of which are human in characteristic, except the mentioned blood (what human characteristics his copper blood has is unknown).
So, basically, you're saying, it doesn't matter what real biology says, Star Trek is right in the confines of its own universe, even if it 1)is self-contradictory, 2)seriously undercuts drama, and 3)contravenes the best theories that explain how
anything lives.
To the best of my knowledge, the
only cases of children between two different species arising incontrovertibly through purely natural means are the ones involving Cardassians and Bajorans, which is neatly explained by a shared,
recent biological ancestry. If there's a bit in VOY where Seska has a kid with a Kazon, I am unaware of it, and dearly hope that's not true.
I understand this is a long post and that you may or may not be reading by this point, so I will try to briefly restate my logic on this:
Argument 1:
Major premise: Pon farr is a biological process.
Minor premise: Biological processes are subject to selection pressures which favor organisms that can successfully reproduce.
Conclusion: Pon farr persists to ensure that Vulcans can successfully reproduce.
Major premise: Outside medical intervention, two species with radically different coding mechanisms and biochemistries are unlikely to conceive a viable offspring.
Minor premise: Vulcans and humans have radically different coding mechanisms and biochemistries.
Conclusion: Vulcans and humans are unlikely to conceive viable offspring.
Major premise: Selection pressures ensure that mating drives generally drive an organism to achieve union with an organism who is capable of providing it viable offspring.
Minor premise: Pon farr persists to ensure that Vulcans can successfully reproduce.
Conclusion: Pon farr should drive a Vulcan to seek a Vulcan mate.
Argument 2:
Major premise: Spock would never wilfully betray Starfleet if any other option were available.
Minor premise: Spock betrayed Starfleet during pon farr.
Conclusion: Pon farr did not leave Spock any available options (i.e., Christine Chapel, real dolls, socks, chemical treatments, intense meditation, hologram wives, Voyager technobabble, Ensign Ricky's taut young body, whatever).
Now if these premises are untrue, the logical scaffold collapses, of course, but I believe them to be true. As far as an explanatory framework, I think it works quite well.
I think our sticking point might be the major premise to syllogism three--"Spock would never wilfully betray Starfleet." The only other alternative is a set of syllogisms that goes:
"Major premise: Spock would betray Starfleet when not betraying Starfleet is a viable course of action.
Minor premise: Spock betrayed Starfleet during pon farr.
Conclusion: Spock values immediate gratification of his urges for T'Pring over his loyalty to Starfleet.
Major premise: A few weeks of enforced chastity or non-preferential sexual activity that will not interfere with the health of an officer does not constitute grounds for an officer to violate his Starfleet oath.
Minor premise: Spock violated his Starfleet oath based on a desire to not undergo a few weeks of enforced chastity or non-preferential sexual activity.
Conclusion: Spock injustifiably violated his oath."