It's not even merely the idea that some trans dimensional being might choose to communicate with our plane, it's the manner they allegedly chose to communicate: A Ouija board.
The Ouija board is the ultimate self fulfilling prophecy. The humans who place their hands on the planchette can either consciously or subconsciously dictate the messages the purported being on the other end of the board is transmitting.
And I don't even necessarily have a problem with that, but let's be up front about it if we're all going to play a party game that amounts to recreational fiction writing with a spooky feel.
I also don't mean to take anything away from anyone who feels they have benefited from the Seth material. Inspiration can be drawn from many sources reputable and not.
I just wonder if the people in that room actually believed what they were purporting to.