For an ordinary Imperial citizen, isn't worshipping Chaos a logical choice?
I'm sure somewhere in the lore there are places with heavenly living conditions, but for most Imperial citizens, life is incredibly miserable. No one cares about you, no one cares if you live or die, and no one cares about your family. Under these conditions, being loyal to the Imperium doesn't make you a good person; it just shows that you're an idiot. Why would an ordinary person say, "Oh, I should keep protecting this system that promises me nothing"? With Chaos, at least you have the hope of climbing the hierarchy, a chance to achieve some power, or if nothing else, the chance to take revenge on the people who condemned you to these conditions. It's like choosing between two buttons: one offers certain death, and the other offers certain death plus a cotton candy. Even if the reward is incredibly low, at least one of them promises something a little extra. I'm talking about ordinary people, not those at the top of the pyramid like the Space Marines or nobles.