User blog comment:- Darkchylde/Acnologia's Element?/@comment-173.87.12.242-20141211055642/@comment-7418318-20141211231813

The anti-Human faciton of the Dragons considered the Humans as nothing but animals and food. They didn't recogize them as a sentient species. Does that make them generally evil? That's a matter of opinion.

Did the people and even others of their own kind (i.e. the pro-Human faciton) consider them evil? Apparently so.

Thus the quotation marks around evil, not because it's my opinion, but because it's the general opinion of the people within the story (those few that know about it anyway).

And yes, we do not know what happened to Acnologia before, during and after the transformation, but ultimately it doesn't matter much, because there can be no justification for his actions.

While for the other Dragons there was the excuse that they see Humans as just animals and just don't know better, but with him once being Human that argument doesn't count for Acnologia. He knows Humans are sentient and still he enjoyed tormenting them for fun before killing them without provocation. No matter how bad he had it in the past, nothing can justify that.