Sarcasm is an adjusted stress reaction.

It's not just SF, there's also the very dodgy pattern in Buffy and Angel where characters who are depicted as taking the fight against evil too far and bigotedly persecuting harmless supernatural beings always seem to be African-American men (Forrest Gates in the Initiative arc, Gio in "That Old Gang of Mine", and to a degree Robin Wood). And I still resent that Supernatural episode with the vampires trying not to kill people and the bigoted human villain who seemed intentionally and pointedly created as "Evil Charles Gunn".