It seems like this is counteracted by the rationalist tendency to focus on what world-states we want, not just what options make us feel good when we think about them. If we care about someone else's "stress" but not someone else's "elevated adrenaline, cortisol and associated problems," that's a problem with our caring.
Phrasing it in terms of "stress" suggests the solution is to, e.g., take them out of stressful environments, etc. Phrasing it in terms of "elevated hormones", suggests solutions like of anti-hormonal/anti-stress drugs.
If this doesn't bother you, apply the same logic to "happiness".
steven0461 (comment under "Preference For (Many) Future Worlds"):
Yvain (Behaviorism: Beware Anthropomorphizing Humans):
Eliezer (Sympathetic Minds):
So, what if, the more we understand something, the less we tend to anthropomorphize it, and the less we empathize/sympathize with it? See this post for some possible examples of this. Or consider Yvain's blue-minimizing robot. At first we might empathize or even sympathize with its apparent goal of minimizing blue, at least until we understand that it's just a dumb program. We still sympathize with the predicament of the human-level side module inside that robot, but maybe only until we can understand it as something besides a "human level intelligence"? Should we keep carrying forward behaviorism's program of de-anthropomorphizing humans, knowing that it might (or probably will) reduce our level of empathy/sympathy towards others?