Essentially spiritualists reject all established and proven religions because each and every one is demanding of its participants. This doesn't mean that you can't skimp and become only a once a month Catholic or Protestant or Hindi or Buddhist.
But it does mean that being a real and a dedicated member requires an immense amount of real self-examination, true self-criticism, and EFFORT. Spiritualists dump all that for any 'feel-good' religion-like nostrum that comes down the pike; because being a GOOD spiritualist requires precisely ZERO effort.