> That said, I think your definition highlights the problem: By telling someone it's okay to feel the emotion, you've implicitly endorsed the response.
This tells me that you've not understood my meaning. One is not condoning or endorsing any behavioral response when they say the emotional response (which motivated the behavior) is valid and natural. They are distinct things and one does not necessarily follow or precede the other.
> their reaction is not actually appropriate or okay
I suspect we are talking past each other here. If "their reaction" refers to their emotions, that is not your concern; to think otherwise is wildly antisocial. If it instead refers to their actions and/or behaviors, you simply are not bemoaning emotional validation.
>> emotional response (which motivated the behavior) is valid and natural.
This is obviously nonsense. If an old woman falls over and breaks her knee, and one's emotional response is happiness - they have real problems - it's not natural or valid to feel that. If the idea of choking women to death makes one feel excited - no it's not natural or valid to feel that emotion, they have serious problems. One could go on.
Maybe you haven't met any really bad people in life - when you do you will often find they have very strange emotional responses to things.