It's all the chaos gods' fault. They snatched Big E's babies in the first place.
Imagine what would have happened had things gone to plan from the start, the Emperor and his 20 sons going across the galaxy reunifying mankind. The chaos gods would have had their shit thoroughly pushed in.
This is of course assuming that papa Emps would have raised his children better than they were raised by the various people who found them.
But since Malcador was around, I think he would have kept things in check with the kids.