There is a famous theorem by a Mathematician Godel. In short it says that
Which means that there will statements in such systems which cannot be proved within the system. We as a human being understand that those statements are true in that system but by using rules of inference present within the system we cannot prove the truth/falsity of such statements.
Now my point is this. Kuran/Bible [or any other holy book] can be considered to be sets of axioms and rules of inference. It is a System. It is supposed to govern human behaviour. In short it is supposed to govern human brains. Since our human brains cannot be modeled by any System [defined as sets of axioms and rules of inference]. This means human understanding/ behaviour is beyond any System. Then how can a System (i.e. Kuran/Bible) be relied upon to govern a non-System (human being) in a reliable way. There will be situations in which the System (i.e Holy book or Kuran) will not be able to judge truth/falsity (or appropriate/inappropriateness) of a human behaviour. A human brain itself is so complex. Think about how complex the interactions between 6 billion human beings will be. Also thrown in the complexity of the environment itself with which we are interacting.
Considering the above points, I think it will be foolish for human beings to rely on a code of conduct or a holy book for ratifying/validating their behaviour. Because such a book won't be able to cover all the myriad different interactions in human society