Bah, I'm incoherent in the morning, let's try that again.
It's not that hers is more valid than his, it's that he dismisses hers out-of-hand as having no validity; that he presents his views not as his views or the local way of doing things, but as absolute truth. He doesn't say, "we don't kill, and if you want to live here you'll have to respect that," he says "Killing is wrong." He doesn't say "I was raised to believe in monogamy," he says "Love is between two people." He then goes on to say "OMG your culture is strange and freakish."
Kory reminds him he's full of shit and Tamaran is no stranger than Earth, and rightly so, but she shouldn't have to. Part of any meaningful relationship is respect, and if he wants to be with her, he needs to *respect* her culture and that her perspective is as valid to her as his is to him. But he consistently asserts his own worldview as not just a perspective, but The Only Way, and his behavior as not just the way he does things, but as the Way Things Must Be Done. Their relationship had a constant theme of her changing for him, giving up herself and her heritage for him, and having to *stop being herself* in a way that Dick did not that has never sat well with me. Kory herself may not be particularly perturbed here - "oh, that's just Dick insulting my people again, I'll chide him gently" - but as a third party, I'm still really unimpressed, and not liable to root for them.