Probably something along the lines of "wow, this just sounds like he's reciting that book God Delusion by Richard Dawkins"?
Sorry, not a fan of Last Church, just sounded like fanfic of some new teen atheist. Instead of going into the actual reasons for the Imperial Truth (there are powers out there that use religion for their own nefarious purposes, by denying them worship we weaken them), the Emperor just parrots the usual "but you can't prove God exists therefore he doesn't, checkmate theists!"
Yes it was lazy writing. It tried to attach itself to nu atheism which was all the rage at the time. I’m not generally a fan of my fiction trying to reflect today’s political trends.
I didn't see it that way but its a good point. I saw it more as him not wanting to even really hint at individual sentient powers even as a possibility to people who don't know how the warp/ chaos works. Those that do either he recruits them if they are not corrupted or just destroys them if they are/ likely to fall later. Otherwise, using other understood established concepts to debate/ explain makes sense. Also I think Valdor is switched on enough to work out why psykers aren't in the custodes, so we won't see much there.