It's easy in hindsight to see these types of things as being ridiculous and obviously bunk. We do have the equivalents today, although YMMV on what you think is the modern day "mesmerism".
Why wouldn't today's "mesmerisms" be just as ridiculous? I don't think the mockery is about "absurd things people back then believed" but about "gullible people who will believe all sorts of things".
I think Conan Doyle was a very gullible man for his time. He would have been gullible for today's quakery if he was still alive.
They may started as legit investigations but I doubt they did not realise soon it was a dead end and still keep selling seances and look for funds to keep their research.
I think Conan Doyle was a very gullible man for his time. He would have been gullible for today's quakery if he was still alive.