User blog comment:FairyRaven/Fairy Tail Chapter 391: Gray vs. Silver, Review and Commentary/@comment-24784846-20140704210129/@comment-24784846-20140705134242

Nick, I think the problem everyone has it that because he's a demon in a dark guild filled with demons, its kinda odd how Silviora hasn't turned on anyone yet, because he can definitely beat the other demon gates, maybe not Keith, we haven't seen his latent power yet but Jackal, Torafusa, and Sayla, Kyouka could lose to him. If you think about it, that messes up the power-balance because if someone can use demon-slaying magic in a guild of demons, that not good for the remaining members.

Also yeah, it was confirmed that Tartarus demons are Etherius(Zeref's demons), maybe they are different from the Galuna demons. I am not so sure about the war theory, seems to one-sided