The union of political power and religious authority is always pernicious. For those who are familiar with Christian scripture, this is precisely the meaning of “Render to Caesar the things that are Caesar’s, and to God the things that are God’s”.
Although in the West we tend to think mostly about the past and present influence of the Christian churches on the state, we have seen this unholy mix among Buddhists, since the times of the Indian Emperor Ashoka.
The impulse to theocratic rule has always been accompanied by intolerance for dissent and persecution of minorities, whether in Tibet, Japan, Burma, Sri Lanka, or Thailand. One cannot exercise religious authority and political power simultaneously, as one will always place the former in the service of the latter.
The separation of church and state is not a only social imperative; it is a spiritual necessity.