Although he was agreeing with you at the time, Christopher seems to also share this view of humanoids like the Cardassians being purely human in terms of psychology, and not having significant evolutionary differences in behavior:
Basically, "alien" cultures in ST are like nonexistent human cultures. They all fall within the range of known human behaviors and beliefs, but there are variations that make them exotic to the typical viewer or reader, at least the Western viewer or reader.
"fall within the range of known human behaviors and beliefs"
Garak may say Cardassians and different in biology - and Voyager may have said Vulcan's posses glands that supress emotional response - but it seems the overall effect must be to produce identical psychologies - with only the culture being different - as unlikely as that seems.
Yes, alien cultures having a similar range of behaviours and beliefs to humans would indeed appear to imply very similar or basically compatable psychologies/neurologies. For those cultures to fall within the range of known human behaviours neccessitates a shared standard of psychological and so presumably neurological construction, I certainly acknowledge this. As I said, I agree entirely the Trek aliens- Humanoids in particular-are indeed essentially human in their thinking and behaviour. However, that doesn't mean they aren't "exoticized" in places by a few significant alien additions, including perhaps a different perception of memory or self recognition resulting from slightly altered neurology, as ASiT implies to a limited extent about Cardassians. The base psychological template is there, but there might be a bit of imaginative tinkering that wouldn't result in the cultural traits intended to result from this mode of thinking becoming too inhuman and thus inaccessible. I essentially agree with you, I'm just cautious about saying "they're human, that's all, end of story" when I think more thought often goes into it than that.