My thoughts are that you can read not to feed them any specific thing, including many of the favorite things many of us give them as treats. No matter what you feed them or how you manage them somebody can find something wrong with it. That's especially true of anything you feed them.
Corn, like any other grain, is high in carbohydrates. It has fiber, protein, minerals, and fat. Corn is a grain that fueled and sustained different civilizations, like rice fueled some civilizations, rye fueled some, wheat fueled some.
If you feed too much of anything other than their chicken feed they will not have a balanced diet. If they mostly live on chicken feed that feed contains what they need. Most of what they eat needs to be that feed. There is a rule of thumb that anything other than their normal feed should be limited to no more than 10% of their diet. There is no science behind that 10% that I am aware of, just a general guideline so you don't overdo it too much. My personal preference is to not give them the same treat every day but to vary it so the nutritional value of their treats vary.
If your chickens forage for a lot of what they eat you have given up the ability to micromanage what they eat. They are pretty good at balancing their own diet when given adequate choices. I'd still try to avoid giving them the same treat every day and not give too much. I violate that though. When I'm canning or freezing something out of the garden or orchard they may get a lot of scraps in one day. When I'm cleaning out the garden they may get a lot of one thing. But that is not day after day after day. That is a one day overload, then they may not see any of that specific thing for a long time. But they will see something different.
