Remember that while separation of church and state in the US founding was similar to the Bismarkian secularism ~ denominations dominating different states thinking they were safer from being on the losing end if no establishment religion was allowed ~ there was also a strand in the separation of church and state which supported it as much to protect churches from the corrupting influence of being the state church as to protect the state from being dominated by religion.

There's a twin movement in weakening the religious hold on society under an establishment church, in that the establishment church works to undermine the strength of rival churches, and being the establishment church tends to weaken the appeal of the establishment church over the long term.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.