This guy says:
"Ever since Victorian times, atheists and agnostics had thought of themselves as honorary Protestants. Atheists saw a common ally when Protestants attacked the Catholic Church. Many Atheists took up arms with the Protestants..
John Stuart Mill, for example, recalled his atheist father urging him â€˜to take the strongest interest in the Reformation, as the great and decisive contest against priestly tyranny for liberty of thoughtâ€™. Later in the century Thomas Henry Huxley, inventor of â€˜agnosticismâ€™ and preacher of evolution, said his agenda was rooted in â€˜that conviction of the supremacy of private judgmentâ€¦which is the foundation of the Protestant Reformation."
So he said Atheists in a way joined forces with Protestants to overthrow the Catholic Church. Atheist and Protestant was almost at one time indistinguishable