But who decides which rules are neutral? Even this is relative and subjective. Laws are not inherently neutral. A pH of 7 is only neutral because it is bounded by 0 on the left and 14 on the right. In a different system, perhaps it would be from 10 to 30 and thus a pH of 20 would be neutral.
The closest we have to a "neutral rule" is "The Golden Rule":
"Treat others as you would like them to treat you."
It has a long history, both secular and religious. Pretty well everything flows from it, and if someone is doing "the wrong thing" whilst claiming to obey it then they are probably deluding themself.
The rule is suited to enforcement, since if someone does something "wrong", rather than immediately attacking them you can reasonably ask "Would you like it if I did this to you?". Limitation of power is built in.
> But who decides which rules are neutral
You’re correct that rules are themselves to an high degree arbitrary. They can only be imposed by a source of authority that’s beyond question: God(s), elders, founding fathers, kings, etc. In the case of the U.S. it’s historical inertia going back to 1215.
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In that example the number on the scale is less important than chemical properties of the solution. Reality is that which, when you stop believing in it, doesn't go away and all that.