By definition, it is evolved biological behavior to get an immediate fear response to outsiders, in the evolutionary and, until the invention of antibiotics 50+ years ago, recent history outsiders carried new sources of infection that could wipe out populations, villages, families, socieities. Let remember the America’s indians responses to European diseases and the plague. More recent examples are Ebola and Zika, the 1915 flu pandemic.
“…if Arendt is correct, we are all capable of perpetrating evil against an “other,” since we are all capable of living unreflectively.”
I would call it living, instantly, instinctively, automatically and completely unconsciously according to biological imperatives of survival and reproduction. Biological impulses and instincts that were set into our genes eons ago!
“The only defense is clear and critical thought, where “thought” must be, in part, defined by the ability to think from the other’s perspective…”
This (very old fashioned) Enlightenment ideal about “thinking” is naive and uninformed now that we have more information on how behavior is caused. This is similar to telling people who have a medical condition, mental illness and addictions to just — “think.” the behavior is caused by specific and detailed brain mechanisms which we now are starting to understand.