This is a question where fiction might give us more insight than fact. If you read realistic novels from the 19th century you will find right away that many of the characters are atheists or agnostics. The gold standard novel is War and Peace which contains only one overtly religious character (Maria Bolkonskaya) if I recall correctly. More than one of the characters is overtly atheist. Tolstoy could put this into fiction when his counterparts in the Physics department and the Philosophy department and the Political Science department would not dare to say it.