If the chaos gods are real and are REALLY manifesting their gifts onto people in 40k. What is the emperor doing? As a human in the military of the imperium, what proof do I have that the emperor is doing anything at all to stop chaos? He isn't making space marines grow wings or manifesting miracles. Whereas, you can see a chaos mother fucker miraculously spawn giant talons or whatever to rip you a new asshole. The Imperium would have a far easier time getting people to believe if some actual wild positive shit would just happen. Yet it all boils down to "Yeah man, just use your lasgun against this chaos daemon and pray to the emperor(who don't answer you.)" Meanwhile chaos people spawning guns out of orifice on their bodies etc.