Not to repeat myself, though apparently it's necessary: Kirk agreed with Janice. We know good and well that Janice didn't just want to be Kirk's lover, she wanted to be a starship captain. The episode doesn't make sense, unless it's about the glass ceiling.
Or he felt it pointless to argue with someone who is known to be nuts and also apparently very ill. It's safe to assume this isn't the first time the subject was discussed and probably argued. After a while you're tired of the subject and just shrug it off with, "Fine, whatever."