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Secular liberalism

The French philosopher Voltaire noted in his book on English society, Letters on the English, that freedom of religion in a diverse society was deeply important to maintaining peace in that country. That it was also important in understanding why England at that time was more prosperous in comparison to the country's less religiously tolerant European neighbours.

If one religion only were allowed in England, the Government would very possibly become arbitrary; if there were but two, the people would cut one another’s throats; but as there are such a multitude, they all live happy and in peace.

Adam Smith, in his book The Wealth of Nations (using an argument first put forward by his friend and contemporary David Hume), states that in the long run it is in the best interests of society as a whole and the civil magistrate (government) in particular to allow people to freely choose their own religion, as it helps prevent civil unrest and reduces intolerance. So long as there are enough religions and/or religious sects operating freely in a society then they are all compelled to moderate their more controversial and violent teachings, so as to be more appealing to more people and so have an easier time attracting new converts. It is this free competition amongst religious sects for converts that ensures stability and tranquillity in the long run.

Smith also points out that laws that prevent religious freedom and seek to preserve the power and belief in a particular religion will, in the long run, only serve to weaken and corrupt that religion, as its leaders and preachers become complacent, disconnected and unpractised in their ability to seek and win over new converts:

The interested and active zeal of religious teachers can be dangerous and troublesome only where there is either but one sect tolerated in the society, or where the whole of a large society is divided into two or three great sects; the teachers of each acting by concert, and under a regular discipline and subordination. But that zeal must be altogether innocent, where the society is divided into two or three hundred, or, perhaps, into as many thousand small sects, of which no one could be considerable enough to disturb the public tranquillity. The teachers of each sect, seeing themselves surrounded on all sides with more adversaries than friends, would be obliged to learn that candour and moderation which are so seldom to be found among the teachers of those great sects.