Forbin said:
But his subconscious summoning of Ruth on the SL planet tells me that Ruth, not Carol, is the woman Kirk most regrets leaving behind.
No, I think Kirk came upon a flower or something and it reminded him of Ruth, that's why he thought of her at that time.
Now if he had stepped in some cow dung, maybe it would've reminded him of Sally Mae, the farmer's daughter he used to doink in his younger days.
Strange Hollywood thinking.
In this case, it was an easy kill for the story writers, someone about whom people cared only a bit, being new, but something that would be good for giving a major character major pain.