Do you support the legalisation of polyagmy and polyandry

[Vincenzo Vinny G.]

But why justice and fairness?

Because we've assigned a positive value to these things.

And why not other values, like force or authoritarianism

Similar to the above but in the reverse.

Sorry, but just because you assign a positive value to these things does not make them valuable.

It only makes them valuable to the people who have assigned them this particular value.

If someone chooses not to assign them the value you do, they exercise their right to reject your valuation and therefore reject your moral codes.

And startlingly (for you, anyway), they have as much of a right to assign value x as you have assigned value y. Your valuation is not more important or more valuable than theirs.

And therefore, you are left in a position where you can enforce no moral laws by taking these valuations into consideration.