If you or your group had misconceptions about the terrible responsibility/curse that being a psyker was, your gm should have educated you earlier about what horrors a psyker was capable of. I did this to my group earlier on. Their fourth mission was cleaning up after a psyker from another cell screwed up and got "warp whispers". It was up to the PC's to head up investigations into who had been in the area at the time and to help the kill-squad track them down. They didn't ever go in with them for the kill wanting to keep their hands clean of the blood of women and children but they still got to see what happened to innocent citizens who were just suspected of being in the wrong place at the wrong time: wrong place being any where near a psyker and wrong time being any time the psyker gets it in their head to use their powers.