This is so obvious that a person of intelligence like yourself risks a loss of credibility for posturing as if you do not see the difference.
But just in case you truly do not, allow me to explain. The use of a first name is most often a token of felt closeness, of familial affection, of camaraderie. When a person who genuinely likes and respects Sarah uses her first name, there is no cognitive dissonance. The usage “feels” right, because it matches the cultural template for an expression of affinity.
Whereas when someone like McGuinniss uses the familiar names of the family to whom he is a predator, there is no affection, no sense of family, no personal affinity, only predation. The usage is as jarring as if a rough-looking total stranger driving an old van approached your young daughter at the play ground and called her by her first name. What does your cultural template tell you about that? Creepy? At a minimum.
BTTT - absolutely excellent.
Aside from the fact that when she introduces herself, she calls herself Sarah to us.
Sheeesh.