He helped fight fraud:

[Houdini] came out swinging when spiritualism—the belief that the dead could communicate with the living—spawned racketeers who robbed the bereaved. Houdini’s own mother had recently died. He felt the vulnerability that death brings. So when he saw people exploiting it, he went into a white-hot rage.

He toured the country with a team of undercover investigators (sometimes even attending sé­ances in disguise). Then during his stage shows he called out the local spook-crooks by name, listed their crimes, and exposed their methods. The Spiritualist mafia responded with death threats. Houdini answered by lobbying Congress for stronger anti-fraud laws.