Leaders in countries where religion is still the rule of conduct are considered as representatives of God and should act according to his teachings.
Conceding that politicians should do God, it remains which God teachings they should follow, especially in multi-faith societies.
Politicians aren’t perfect people. They are prone to mistakes and weaknesses and thus they can’t do God. This conflicts with democratic values as politicians should do what people , not what God, ask them to do.
Turning politicians into God-figures means they can be above reproach and anyone opposing them will be punished.
There are enough God-figures around the world in dictatorial regimes as in North Korea. Currently the world needs much less of them, not more.
Religion if incorporated into politics can be used as a tool to repress different views. There are theocratic regimes which stifle all sorts of freedoms in the name of religion whose teachings they interpret according to their scheme to hold to power.
The excess of incorporating religion in politics will turn Christian countries to the Puritan era as it can turn Muslim countries to Taliban rule.
Religion should remain an individual matter; especially, in multi-faith societies. Imposing a unique brand of religion is likely to cause a clash among sections of society with different religious views and beliefs.
Any country should have a constitution that guarantees democratic values. Empowering religious institutions over the democratically elected ones will turn societies into theocratic where religious dissent can lead to persecution. As such, multi-faith societies should be governed by secular laws and religion should remain a personal matter.