To give an idea of how fucked you are if you're a psyker -
There's a bit of old fluff dating back from...4th edition, I think, about how demons perceive the world from the warp.
To them, every mortal soul shows up as a speck of light.
Except for psykers. Their souls show up as massive stars, and the stronger they are, the bigger it is.
So every demon knows exactly where you are, because they can see you and are drawn to you.
You're basically born with the Mark of Sacrifice from Berserk, except you don't get Skull Knight, you don't get Dragonslayer, and you certainly don't get plot armour.
Oh, and whenever you use those powers you have, which you would think would be the one good thing about being a psyker, you're basically spreading your metaphysical buttcheeks apart and inviting them to hop in.
So yeah, being a psyker sucks, and that's not even getting into the cultural stigma that the IoM feels towards them, because as it turns out, not many people trust those who can spontaneously turn into a demonic flesh portal.