As has been pointed out, the entire Koss-T'Pol marriage isn't very logical when you boil it down and look at it. T'Pol is a major renegade in Vulcan eyes and has already rejected one "get your ass back here or the marriage is off" communication from the Koss-parents. Then there's the whole P'Jem thing which she's blamed for. Throw in the fact that she quit her job to run off with humans on what was considered an illogical expedition and now she's brought a human home to meet her mother and you get a picture of sheer illogic. They would have to be concerned that this illogic on T'Pol's part might be some sort of genetic abnormality (which evidently it was if the showrunner's season 5 plans of revealing her to be half-Romulan bore fruit) which would likely cause concern that it might be passed on to any offspring.
So why would Koss (& family) push forward the marriage? There is no logic in their actions. By publicly tying their family to hers, they are essentially linking themselves with the pariah and painting a big target on their back. For that matter, they probably aren't even sure T'Pol will come back when Koss goes into pon'farr! And then, after she goes back to the human ship, T'Les abandons everything that T'Pol sold away her future for to go hang out in the desert with the Syrannites (which makes me wonder why Koss wouldn't immediately have the marriage annulled.)
Which leads to the various theories:
- Koss has a thing for T'Pol. Understandable - she's hot - but it doesn't work for me really because the way he goes this seems fairly underhanded.
- Koss' family are Syrannites, so they're covering for T'Les. Again, this only partially works for me.
Put simply: he liked T'Les. Not in the Mrs. Robinson way, but as a professor (did they establish what she taught at the Science Academy? Let's just presume he took a couple of her courses and liked her.) So Koss liked T'Les. Thus, Koss saw only one way to protect T'Les and that was by marrying T'Pol, so he pressured her into this marriage. Like all Vulcans, he figured that affection would come in time (although "Home" established pretty clearly that he wasn't ignorant of her ... friendship with the human, Tucker.) After the wedding, they went their separate ways for the time being because that was part of their arrangement, but while in conversation with his family, overheard enough conversations between his parents to realize that they were scum. Closely linked to V'Las, they were at least partially responsible for T'Les' ouster at the Academy because they wanted retaliation against her family for the slight T'Pol had given them with the previous marriage rejection. Koss spoke with T'Les about this matter and she bolted to join the Syrannites. After T'Les' death, Koss released T'Pol because he perceived some threat to her from his parents (since they had been linked to V'Las and thus suffered a serious status fall after the Vulcan civil war.)
What are your theories?