[It's a little strange explaining the concept of happiness to what seems to be some sort of doll or robot, but Rose has the sense that she isn't from here either. They're in the same boat, in a way. She has no reason to be cruel to this person who has not yet acted with ill-will towards her.]

A philosophical question for the ages, I'm sure. I would argue that it doesn't make the emotion less "real," per se, but it cheapens it. Certainly, I'm sure that their happiness feels very similar to the happiness of those with the full spectrum of emotional capabilities. Yet to feel one emotion only... cheapens it. You cannot truly enjoy happiness until you have experienced the lack of it.

Also, it is natural for humans to react to situations with feelings other than mindless joy. The fact that they don't express any other emotion is disquieting to those of us not from here.

I hope that explanation is somewhat clear?