User blog comment:B214/Chapter 504: Rift/@comment-4945830-20161002203645/@comment-1776824-20161003165257

Gray is definitely smarter than this, but his current state of mind prevents him from being able to form coherent thought processes and connections. If you factor in his increasing corruption at the hands of his magic, it gets worse. Your argument is based on the normal Gray hearing this information, not the Gray who had Juvia die and then find out his best friend was the strongest of Zeref's demons. That's my issue with people's criticisms: "Oh, Gray should understand this," or, "Gray knows better." Well, the fact of the matter is that right now, no, he doesn't. For the what feels like hundredth time, Gray is currently in an emotional tizzy. He isn't processing things the way he should for various reasons, and that is what is leading to this pointless, honestly quite strange conflict. That, and Gray has no knowledge of the truth behind E.N.D. except that he is Natsu and that he is Zeref's brother.