User blog comment:Miskos3/Fairy Tail 522 & 523: Gray's Trump Card & Is Destiny Burning, Review/@comment-31.132.65.54-20170218162605/@comment-7418318-20170220070254

The difference is between Ur and Ultear on one side and Gray on the other is the existence of alternatives.

Ur had no choice. It was Iced Shell or dying together with her pupils. She tried to fight Deliora and lost. She couldn't beat it and the chances of them escaping alive if they made a run for it were pretty much non-existant.

In Ultear's case people had already died and kept dying all around her. It was literally an apocalypse and as far as she knew there was no way to win this fight and stop the dying. So again there wasn't really another choice for her. On top of that we have the whole redemption matter. She had legitimate reasons for her guilt. She killed countless people while in GH. Sure she followed orders, but she wasn't forced to follow those orders, but chose to do so for the sake of her own selfish ambitions. After Last Ages we see that weight being at the very least strongly alleviated if not outright lifted from her shoulders. I really can't think of anything other than Last Ages (or outright sacrificing her life) that might have made her consider herself redeemed. In that way alone it was already worth it for her, which is also why she never regretted casting Last Ages. She might not be universally happy, but she sure is a hell of a lot happier than she ever was since being seperated from her mother.

Gray? Sure sealing Zeref and having everyone forget about their grief would work, but at this point there still are other options left to them. So far only Natsu even tried to attack Zeref himself, but apart from Happy and Natsu himself, nobody in FT knows how that attempt worked out. And with him merely trying and failing to kill a single person he doesn't have a real need for sacrificing himself for redemption's sake either.