@Smoothralph sadly, I think people's theories are right, and they did it solely to stop Rocks from murdering his family.Â
Apparently, didn't stop Xebec from murdering his wife though. Explains why whitebeard took him in; DOESN'T explain why teach us such a completely self-centered, backstabbing, glutinous bas****. I feel like he's the complete opposite of his father. Not that Xebec was any kind of hero or anything, but when he saw Injustice, he wanted to END.