BONUS QUESTION: Can a religiously and ideologically diverse society be a fair or just society if its laws are based on morals, views, and opinions unique to just one group within that society?
It doesn't matter if a society is 2 people or 2 billion, the only thing that should be legislated is morality. But...no religion I know of sticks to an actual, universally applicable moral code. Instead, they pile all kinds of "moral" precepts like no gathering sticks on Sunday, no sex outside of marriage or honor killings, onto their tenets of morality.
Using those examples, liberals and conservatives alike want
their moral code to be the law of the universe. But there is near universal (98%+) desire a goal for good order, which only excludes tyrants and anarchists. From that, we can deduce a moral code which can be applied to us all, while declaring the right to be a tyrant or an anarchist simply doesn't exist because their goal is the violation of any of the rights of the rest of us.
So what is such a moral code? Simple, turns out to be a refined version of the Golden Rule, which is buried deep within almost every religion on Earth. To wit:
Morality is honoring the EQUAL rights of ALL people to their life, liberty, property and self-defense, to be free from violation through force or fraud. And of course these rights apply even to tyrants, anarchists and other criminals who haven't yet violated or threatened to violate said code.
All else is individually determined virtue, which should not be legislated, though it is subject to public, non-violent pressure.