Effectively, only an atheist regime can guarantee religious tolerance:
"Marx’s analysis of the political imbroglio of the French Revolution of 1848 comes to mind. The ruling Party of Order was the coalition of the two royalist wings, the Bourbons and the Orleanists. The two parties were, by definition, unable to find a common denominator in their royalism, since one cannot be a royalist in general, only a supporter of a particular royal house, so the only way for the two to unite was under the banner of the ‘anonymous kingdom of the Republic’. In other words, the only way to be a royalist in general is to be a republican. The same is true of religion. One cannot be religious in general: one can only believe in a particular god, or gods, to the detriment of others. The failure of all attempts to unite religions shows that the only way to be religious in general is under the banner of the ‘anonymous religion of atheism’. Effectively, only an atheist regime can guarantee religious tolerance: the moment this atheist frame disappears, factional struggle among different religions will explode. Although fundamentalist Islamists all attack the godless West, the worst struggles go on between them (IS focuses on killing Shia Muslims)."
― Slavoj Žižek, Sinicisation
Barricades in the streets of Paris (French Revolution of 1848)