The real rule is something like "This is my fellow human being." or even "This is my fellow living creature." Something like a kinship of shared existence. I don't know. The being I'm interacting with and the experience they are having has value. That value is innate and I care. I doesn't matter if I should or should not. Empathing is my default setting. I can shut it off, but it requires conscious effort to do so. People's feelings are as real to me as a scent in the air.
I would imagine this would be even more the case for those with dominant Fe.