SSK_Toronto mentioned romance languages.
In Spanish derecho means "right side", but also "upright", "straight ahead","judicial right", "duties", and "fairness".
In English the word u"upright" means "marked by strong moral rectitude <an upright citizen>" (Merriam Webster) and "rectitude" means : 1. the quality or state of being straight, 2. moral integrity : righteousness, 3. the quality or state of being correct in judgment or procedure."
They define "downright" as "1. archaic : straight down, 2. absolutely 1 <downright handsome> <downright mean>"
"Forthright" a : "directly forward, b : without hesitation : frankly"
The large majority of people are right handed, and the lines they draw with right hand are straight, and the work they do with right hand is well done. To treat others fairly, you need to perform in a competent, experienced way, like the work you do with your right hand, and not with the inferior competence of work done with the left hand.