You never know like in that one episode when they go to an alternate dimension where they had all the same characters but they were the regular characters opposites
You mean edolas?
Acnologia is really a good person, he's a doctor of dragons. He care for dragons and humanity, until he was betrayed by them and the dragons killed his family and ruin his town. You see, every villain has a sad past.
Ps. His name isn't really Acnologia though. The name Acnologia is the name of the dragon whom he trusted the most but betrayed him