Let's suppose God has given us perfect laws by which we should govern society. Let us also suppose that God has said that anyone who opposes the implementation of any of those laws is an enemy of God and should be killed.
Would those laws always be properly interpreted and implemented by imperfect men? Of course not. There would be various interpretations; this would lead to much blood shed as different groups of "believers" would say, "We have the correct interpretation of God's law and because you're opposing it you are an enemy of God."
By the way, I'm not against individuals arguing--for example--that a thief's hand should be cut off. What I am against is bypassing debate about individual laws and trying to implement a whole system of law as a block (particularly when violence and deception are used).
Deep down these "believers" know reason is not on their side. They know that they cannot convince the public that particular divinely ordained laws are good; therefore they seek instead to weaken and take over governments through deception and violence. Once achieved all dissenting voices can and will be silenced. (Until such a time as new more committed group arose and implemented God's laws properly--or so they would think.)
So if God did tell us that there are things we should do, is this a problem simply because it came from God, and cannot be questioned?
If God gave people principles (fixed principles if you like), instead of fixed laws, then people would be free to discuss and debate within the framework of those principles. If the principles were good (e.g. Do to others as you would have them do to you), then the society which sought to uphold such principles would move towards democracy, eventually obtain it, then value it. Instead of saying a thief must have his or her hand cut off, such a society would debate what is the best punishment for a thief, which punishment most satisfies victims, and which is best for society as a whole.
And just to be clear, I'm not against a theocracy where there are fixed laws, if those laws were implemented and directly enforced by God without the help of men. The only way a perfect law from God could be enforced the way it was meant to be enforced--without society tearing itself apart--is if a perfectly just, fair, kind and all powerful being enforced it.
Until such a time as God shows up and rules by his own hand we must be ruled by principles and not seek to implement a theocracy. (If God is as George MacDonald describes him in Justice, such a rule would not be a bad thing.)
Note: I need to make something clear. I'm not against implementing a law which can be found in a religious text if that law happens to be a good law. The punishment for perjury in the Mosaic law happens to be a very good. As is the law and punishment regarding theft (See Exodus 22). If those kinds of punishments were adopted for theft the prison population would be greatly reduced, victims would be reimbursed and many children would have their fathers back.