Reign of Terror during the French revolution was neither secular nor atheistic. They have state religion 'Cult of the Supreme Being', which was deistic. Robespierre himself was deist and opposed to atheism.
Ok, I'll not argue about that even if I still think the topic is arguable.
Anyways in case you are right it probably makes GPs point even stronger: when established religions are chased away quasi-religions - and often extremely dangerous ones - take their place.
Here in Czechia power of established religions went away (~ less than 1/3 population is religious). They were partially replaced with folk esoterism (astrology and so), which is much better alternative, as folk esoterism does not have concentrated power of e.g. Catholic Church.
Anyways in case you are right it probably makes GPs point even stronger: when established religions are chased away quasi-religions - and often extremely dangerous ones - take their place.