The religious often use the argument that secular states are obviously undesirable since most of the notorious 20th Century totalitarian regimes were secular; Nazi, Soviet, Mao etc. This is an example of bad logic. These regimes were bad because they were totalitarian, not because they were secular. Suppose all the leaders of these states happened to wear bow-ties. We wouldn't argue that regimes in which the leader wears a bow-tie seem to be undesirable would we? In the discipline called logic there is a formal description for this faux pas; 'correlation doesn't imply causation'. Even if it were true that notoriously bad regimes tend to be secular - many are fundamentally religious - it wouldn't follow that it would be the secularity causing the odour. As I said, it would be the totalitarian nature of the regime causing the stink.
Totalitarian regimes will often chose to be secular in order to negate the political and social influence of the religions. However, the power of some contemporary totalitarian states are wholly integrated with a particular religion; notably with Islam. This can be associated with intolerance of other religions, thus adding to the oppressive nature of the regime. Have secular totalitarian regimes had a history of active repression of religion? In general, the Nazis did not whereas the Soviets certainly did. The point is that there is no reason at all why a basically secular democratic state would, necessarily, need to oppress either its religious or its non-religious population. The Scandinavian countries are exemplars.