The rise of atheism in Europe and some other places has nothing to do with authoritarian regimes though. It is in no way a threat to freedom of religion.
Your argument that it doesn't preclude those policies, is a different one from that other poster, that made a direct link between the two, which is not there.
Your argument was that rising European Athiesm would act as a shield against erosion of Religious Freedoms. I think that's too broad a statement. Arguably, politicians/voters who don't prioritize ANY religious laws are more susceptible to allowing bigotry to flourish through apathy and a 'pox on both houses' political framework. Particularly if it means ignoring bigotry in the pursuit of what's perceived as the greater, secular good.
I would use American Mormonism as an example. The Church as a political-body is hostile to Liberal social policy, but because of a history of bigotry from the wider society because of their beliefs, they're more sympathetic to religious minorities' concerns than the larger Catholic or Protestant populations.
This is my view from a mainly Ameri-centric perspective.