How do you know that? Because of what Orochi said? What makes you think he wasn't born evil or grew up that way because his family themselves were evil? Why are we assuming his family was innocent?
Orochi didn't even care Kaido killed the ones who brainwashed him.
Haven't you heard Doffy's Speech in MF?
There is no Evil or Good or Justice, these things are decided by the Victor
You think Luffy is Good? He is a Pirate, he steals Treasures, Destroys everything in his Path, Fights Governments & Law Enforcers, Endangers Citizens, Doesn't abide to any Laws ... etc
The Bad People in Luffy's Point of View are those who Abandon their Allies/Friends or Use others close to them but that's his Perspective only
Anyone can be Redeemed in One Piece and in any Group you can find Good Apples & Bad Ones (Even among Celestial Dragons, Oda made sure to introduce us to Donquixote Homing)
Then go to Fishmen Island and see the Importance of the Flashback there, Oda made sure to show us two Ways to Fight Evil:
Otohime's Way & Fisher Tiger's Way, both wanted the same thing but chose different Paths
Otohime's wanted to find Peace by being Good towards even the Worst People, while Fisher Tiger wanted to fight them and remove them
And yet look at Reverie Arc, the CD that Otohime saved became a Good Person and completely changed !!!
Oda's Message in One Piece isn't Good vs Evil, that's in other Stories
His Message is World Unity & how to Achieve it, after all it's a Story about Pirates who are clearly the Bad Guys of the Story
Red-Hair Pirates said so in First Chapter ever, they are not Saints or Heroes or whatever, they are Pirates, they Kill, Steal, Dominate, Fight ... etc
