>The authors of the APSR study—Elizabeth Simas and Scott Clifford of the University of Houston and Justin Kirkland of the University of Virginia—have this kind of dynamic in mind when they write, “Polarization is not a consequence of a lack of empathy among the public, but a product of the biased ways in which we experience empathy.”

That's the nugget. According to the study, it seems that people with high empathy are more often people with high empathy towards their in-group...and a lack of empathy for the out-group. I'd argue that it isn't really empathy at all...just a more emotional form of tribalism.