Whenever we talk about the “rules of Islam” it is important to differentiate between what is Guidance and what is legislation; between what is sinful and what is criminal; between what risks Punishment in the Hereafter and what is legally punishable in the Dunya. Technically speaking, if you impose as law that which the Qur’an and Sunnah do not, then you are ‘ruling by other than what Allah has revealed’, even if it is by legally prohibiting something that is Haraam; because not all Haraam things carry prescribed punishments.
The abandonment of such forbidden things is left by Allah and His Messenger to the individual’s conscience, to their own taqwa, and these are not matters of the state. At most, such things are to be enforced through attitudes and social norms, not through the law. If you are going to start legally punishing people, or forcing through state coercion, in matters where enforcement has not been relegated to the state in the Qur’an and Sunnah, then this is, by definition, man-made law, even if its source of inspiration is the Qur’an and Sunnah.
I know that this view may seem controversial. For so long we have taken it as a given that whatever is deemed Haraam, it must also be criminal; but this is a mistake. Islam contains Guidance and it contains Laws; the Laws are quite few, while the amount of Guidance is tremendous. And this is as it should be. If every single matter in the religion were to be enforced by the state, what reward could be expected in the Hereafter for compliance? It should be obvious that, in such a scenario of totalitarian enforcement, you would create an epidemic of hidden hypocrisy in society.
Consider the fact that running away from the battlefield is regarded as one of the greatest possible sins; but we know from the withdrawal of Abdullah bin Ubayy from the Battle of Uhud, that it is a sin one is free to commit without legal punishment. Precisely because of this, Ibn Ubayy’s Nifaq was exposed to all.
You simply have to leave compliance with Islamic Guidance to individual choice for it to be of any value; value to the individual, and value to society. If a matter has been left without a prescribed punishment, it is never going to be an improvement on Divine Law to add one.
What remains, then, for Islamism, is to draft policies, to propose political and economic programs that can improve the lives of the people; not to police them in their religion, not to attempt to impose righteousness upon them.