1) Photo of Harry Houdini (left), bogus medium Margary (center), Scientific American associate editor J. Malcom Bird (rear) and publisher O. D. Munn (right):
2) Society of American Magicians' national historian Tom Ewing had this comment (dated July 16, 2020) about the conspiracy theory that Spiritualists killed Houdini:
The Society is well aware of the conspiracy theories suggesting that fraudulent Spiritualists murdered Houdini, but none of the serious scholars on Houdini believe this to be the case, nor does the S.A.M. It's important to note that Houdini was not against Spiritualists or their religion. He fought against fraudulent Spiritualists who charged grieving people money to “reach” their loved ones in the afterlife through sham seances. His investigations were driven, of course, by his hope of reaching his mother whom he loved very deeply.
This particular floating trumpet was actually made for Houdini's use in his lectures on unmasking mediums. It was presented to Rev. Gordon W. Mattice by Houdini's brother, Hardeen, in 1945. Rev. Mattice, an amateur magician, lived across from Hardeen's home in New York City when he was a boy. Mattice then presented it to Robert Lund, the original founder of the American Museum of Magic in 1975.
Houdini was someone who wanted to believe in Spiritualism but, because of his knowledge as a magician, never found evidence of its existence. No doubt he would have concurred with your conclusions.