To be fair though, that never was much of a conspiracy. Maybe in the United States it was but in the rest of the world I don't think people believe the WMD story, rather, we believed the UN weapons inspectors' story.
I've told and convinced plenty of anti-vaxxers about the magical secret way our body naturally produces antibodies if we expose our body to dead versions of a virus (or, now, things shaped like that virus). They like magic, secrets and nature, they do not like the word vaccine.
I do the same with the word conspiracy, "That is a secret plan by a group to do something harmful". It rolls off the tongue.