I'm sure I not the only one who noticed this.
Back in the end of the Tartaros Arc, we see the guild members gathering back at the crater that was the guild. We see Elfman still upset with himself over almost killing everyone. But Lisanna tries to console him by saying it wasn't his fault.
BUT IT WAS. It's up for debate if he was being controlled by Sayla, but I believe he was in control the whole time. I assume that he was aware of everything and decided in his heart of hearts to kill the guild members in e xchange of his sister. Most likely because he wouldn't be able to handle being the cause of Lisanna's death. Twice. (Well, maybe one because of the events of Edolas, but he was still hurting).
It still doesn't excuse any one of them for brushing this aside, especially Cana, the guild and Marakov. No one at the time was angry with Elfman. What's up with that? Even if they were still recovering the battle with Tartaros, someone should have said something.
Think about it like this. Back in the Fighting Festival Arc, Laxus attempts to destroy the guild for the sake of making it stronger. But nothing happens. Realizing that Fairy Law only destroys those who the user sees as enemies and the fact Laxus cares for everyone in Magnolia, everyone is still alive. After the fight and recuperation, Laxus sees the error of his ways and becomes a better person for it.
That doesn't stop Marakov from giving him the boot. How come Laxus is excommunicated, and has to redeem himself (and eventually join back with Fairy Tail), but nothing happens to Elfman? Hopefully, the Avatar Arc shows Elfman atoning for what he did.
"Aw, Quagmire got away with it and learned nothing -- that's great." - Peter Griffin