Right. I think you've gotten a couple of terms mixed up here.
Pariahs are 'soulless', and their very presence and touch is anathema to psykers and daemonic entities. Fire a psychic blast at a pariah, and they will walk through it like it didn't happen. A side effect of this is a general aura of unease and mistrust aimed at the Pariah. For examples look at the Culexus Assassain (Although their wargear ramps these effects up to 11), the Daemon Huntress' little kid from Inquisitor, or the Distaff from the Eisenhorn series.
'Blunts' has two meanings in 40k.
1 - A derogatory slang term used by some psykers to describe non-psykers.
2 - A being/species which, while not a Pariah, is physically incapable of manifesting psychic abilities, shows -some- resistance to Chaos-based mutation/influence (although chemicals and radioactivity can alter the genome as usual, and the influence resistance is speculative), and is affected by psychic powers normally. In addition to this, their 'soul' is incredibly difficult for warp entities to detect. Where an Eldar Farseer would shine like a star, a regular Human would shine like a campfire, and a Tau would be an ember in the wind. They can be found, and spotted, but provide very little sustenance to Daemons, when there are much better prizes, for much less effort.