There are two fundamental sources of moral standards:
Each has its advantages and disadvantages. The good thing about revelation-based morality is that it removes all dissention. Once God has spoken, that's it. You simply can't argue with God or his representative on earth. And that can make it easier for leaders to control behavior. If people sincerely believe that doing certain things will ensure their entry into heaven—and other behaviors will get them into hell—then most of them will opt to do the right (moral) thing.
If a terrorist thinks he'll get to heaven and have sex with 69 virgins if he blows himself and others to bits—well then, he blows himself and others to bits. Whether or not this actually works will remain a mystery until we all find out in the hereafter. That may be a longer time than most of us want to wait. We just might try to interrupt the guy's behavior, even if it means violating his religious experience.
Obviously, the quality of results with revelation-based morality has a whole lot to do with the competence of God's representative on earth. In addition, you really run into problems when God's different representatives disagree with one another. Just look at the widely varied moral justifications for different beliefs regarding birth control and abortion.
On the other hand, with an empirically-based morality there is a lot more dissention. Since no one has God on his side, he must rely on argument, logic and reasoning to get his moral standard accepted by society. Of course, that is also its advantage. When different moral standards clash they are discussed and tested. A governing body can look at the empirical evidence of previous cultures, develop theories, compare methods, do experiments, and evaluate results.
The Government's fundamental standards must be those traditionally identified by the world's great philosophers: rights, justice, and utility. Those are the standards that could be applied to every society since the beginning of time. They are fundamental, and there usually is no argument about their validity (except that America's right-wing crackpots think that utility is a "radical" moral standard).
In addition, it prevents unscrupulous individuals with hidden agendas from controlling society, simply by referring to their special contact with the divine.
And that, folks, is why government MUST base its laws and judicial decisions on the objective application of the standards of rights (of the individual), justice (between individuals) and utility (the greatest good for the greatest number).