Why did you automatically bring "ethics" into this discussion? The person you replied to was probably using the word 'should' in reference to some other objective.
Someone said, roughly, that X should be like Y.
You immediately asked them why this was ethically optimal.
To me that seems like a non-sequiter.
There is no reason to suspect that the optimization (with respect to whatever objective you desire, e.g. total happiness) of a large, complex, chaotic, system (such as a society) can be best achieved by using 'ethical correctness' as the only criterion for decision making.
At least, that's my opinion. I hope that doesn't make me an indecent human being.
