There's a protein in raw eggs called Avidin. Avidin inactivates biotin which is a vitamin. So another reason not to feed, or allow chickens to eat raw eggs is because it can cause a vitamin deficiency. With all the other good sources of animal protein available, I don't see how feeding eggs back to chickens would be necessary except only to serve someone's convenience.Here's a link to the treats chart:
One warning: If your chickens get the taste of raw eggs, they may decide to help themselves by cracking open a few of their own. Always cook eggs before giving them to your chickens; either hard boiled or scrambled.