User blog comment:B214/Talk About What You Want! 2/@comment-24173056-20140703135106/@comment-1359322-20140703135846

Also Cao Cao isn't a scumbag, he just did what he think was correct. Remember Sacred Gear possessors are discriminated among humans too for their Sacred Gears, for those Sacred Gears possessors with no goals, purpose or friends in life, Cao Cao gave them a goal, purpose and friends under the Hero Faction.

You can say Cao Cao is wrong for fighting Issei and the others, but standing from their POV where normal humans rejected them, fighting supernatural beings as humans are the only option left in life for them.