Religious freedom...

[Mudhammam]

Everyone knows how much influence right and authority in sacred matters have with the common people and how much everyone listens to someone who possesses such authority. I may say that whoever has this power has the greatest control over the people’s minds. Therefore, any body which attempts to remove this authority from the sovereign power, is attempting to divide the government. Conflict and discord, like that which occurred between the kings and priests of the Hebrews in the past, will inevitably ensue and will never be resolved. Indeed, as I said before, anyone who strives to appropriate this authority from the sovereign powers is, in elect, preparing a road to power for himself. For what decisions can sovereigns make if they do not possess this authority? They can assuredly make no decision whatever about war or peace or anything else, if they are obliged to wait upon the opinion of another person to tell them whether the policy they judge to be in the interests of the state is pious or impious. On the contrary, everything will depend upon the decision of the one who possesses the right to judge and decree what is pious and what is impious, what is holy and what is sacrilegious.

Every age has witnessed examples of this kind of dissension. I will adduce just one which is, however, typical of them all. Because this right was conceded to the Pope of Rome without restriction, he gradually began to bring all the kings under his control until finally he ascended to the very pinnacle of supreme power. Henceforward, any ruler who sought to lessen his authority even a little, and especially the German emperors, entirely failed to achieve this; in fact, on the contrary, by attempting it, they enormously further enhanced his authority. However, what no monarch could achieve by fire and the sword, ecclesiastics proved able to accomplish by the sole power of the pen. From this instance alone one readily appreciates the strength and power of this right and how vital it is for sovereigns to retain this authority for themselves alone.

That comes from Baruch Spinoza, writing in 1669, at a time when the devastating consequences of letting religious dogma unduly influence policy was all too painstakingly obvious.