However popular spiritualism was, there was plenty of evidence against it by 1920, and many people did indeed reject it. Thus demonstrating that they were greater rationalists, at least in this area, than Arthur Conan Doyle.

It is easy to judge Socrates now, how ignorant was he about Zeus.

Downvoted for making an unsubstantiated claim that Socrates believed in Zeus. This is sheer clumsiness. You make assumptions about what every ancient Greek must have believed because you underestimate them -- though some of them were indeed rational enough to not believe in Zeus. And then you use that false assumption about false failings to support the argument that we must excuse away Arthur Conan Doyle's real failings.

Also, it's you who argued that A.C. Doyle "was one of the great rationalists of the 19th century" -- that's a rather strong claim that argues he exhibited significantly better reasoning than most of his contemporaries.

If he was taken in by spiritualism, when Houdini wasn't, and he was taken in by crude child-produced fakes of fairies, when many of his contemporaries weren't -- what's even slight evidence that he can be called a rationalist, let alone a great one?

Socrates didn't believe in Zeus- he was executed for atheism and corrupting the youth.

(His Ideal of the Good did have a theistic flavor, but you can't accuse him of believing in the Greek pantheon.)