I think its a bias built around expectations. For some kids who like to rub feces on their faces and have a low IQ, you are just happy if they smell fine and dont disrupt the class. For other kids we assert a normal civilized standard of politeness, cleanliness, and output. If the teachers/administrators mess up too much, maybe the feces smearer gets pushed into a position of influence in the class out of desperation.

To move forward with the metaphor, we had higher standards for a democrat-- or we used to-- and we expect corruption and nastiness from republicans. And when the kids who we know to not have low potential start whining that how come they dont get treated with the tolerance we have of the face feces smearer, they get slapped and told thats not a measure they should be aspiring to. We dont judge ourselves by the lowest common denominator. We strive to live our lives better that that. The slap is a hint not to dwell in the gutter.

edit: and yes, I’m an old person who got slapped plenty growing up. And I grew up just fine and am now a joy to be around. (but yes, maybe rhetorical slapping is best)