“Well at least explain why you want the ice cream," an increasingly frustrated Bryce may say. “You have to have a reason for it, right?"
"You just want me to give a reason?"
"Yeah, it doesn't make sense to me."
"The reason is it tastes good and will make me happy."
"Those don't seem like actual reasons to have ice cream specifically. If I find you something tasty but healthier, you'd have that instead, right?"
"Maybe? But I actually just want the ice cream right now."
"Okay, but let's look at this logically..."
This example seems like it's not proving the point set out; Bryce doesn't seem to be critiquing his partner's desires for something that tastes good and makes her happy(her wants), but rather the action of buying ice cream that fulfills those goals. He's assuming that she also shares a value/desire for good health(which I would say is a reasonable assumption for most people) and Bryce tries to lay out an alternate course of action that would fulfill all those values.
This seems like a specific instance of a broader issue throughout the post, which is that want is sometimes used to mean an intrinsic value and sometimes used to mean an instrumental value, making the treatment of both confused. Intrinsic/terminal values can't be irrational, like you've said, but instrumental values certainly can be. If you have a terminal value of being happy and content in life, I would say that wanting money would be instrumentally irrational value/desire.
In the ice cream narrative above, Bryce is critiquing her instrumental values rather than her terminal values, and in theory I don't see much wrong with that. If she explains her reasoning behind choosing ice cream as a terminal value and Bryce still rejects it, or if it turns out she just intrinsically values eating ice cream, then that is a problem for their relationship.
In fact, I think it's the last two sentences that make the exchange problematic. It seems like she is expressing an illegible preference for ice cream that Bryce is just dismissing.
I agree with that. I think that the general ick that I get from the dialogue is the presumption and general tone of Bryce. Thanks for clarifying!