The real opponents of secularism
I've already argued here previously that the primary de facto opponents of secularism (I'll focus here on the UK) are not the religious literalists and religiously pious. These are few in number and could be easily kept in their place if the majority of our political and opinion-forming classes were principled secularists. So why aren't the powerful secularists?
I will use the political terms "left" and "right" here purely for convenience.
Most of the "right" are conservative (with a small c): they are inclined to the view that nominal religious identity and expressions are relatively harmless and act as a significant civic glue in unifying the population. Their view of religion is really no different to their view of the monarchy. They don't really believe in any principled defence of monarchy, they are pragmatists, comfortable with the status quo or a very cautious gradualism. They see no great harm in socially sanctioned forms of religious hypocrisy and suspect and fear that the great unwashed would become too unpredictable and dangerous if let loose from their historical/religious moorings.
The "left" is rather different. It has recently effectively gone through a period of ideological revisionism. Traditionally a staunch opponent of religion for its promotion of ignorance and its many alliances with reactionary forces, it now finds itself loath to explicitly criticise many non-Christian religious tenets and practices that it historically condemned, since it sees most other religious followers as "victims"; not of their own religion's reactionary dictates, but of western "imperialism" and "injustice" and "exploitation".
The two broad groups, I would argue, represent the primary opponents of secularism. Neither of these groups are themselves particularly religious, that is rather obvious, but they each have different reasons to oppose secularism. What does this mean? It means, among other things, that focusing on the weaknesses of religious/theological ideas and arguments is likely to have only a very modest effect, no matter how brilliant your arguments, because you're effectively attacking the wrong target.
The real target should be the weak points put forward by the essentially non-religious "right" and "left", who, for different reasons, defend the idea of religious privilege. It is they who have the power and influence, and nothing substantial will be achieved without the consent of large numbers of these groups. So the big question is: how do we change the minds of some of these people? Indeed, can we change the minds of many of these people?