Talia Al Ghul Being Evil Is Necessary For Damian's Character Arc

When Damian Wayne made his comic debut in 2006, Talia al Ghul was also characterized differently from how she was before. While many writers prior to mid 2000s portrayed her a sympathetic and even heroic figure to the point that she was considered Batman's main love interest during the Bronze Age instead of Catwoman, Grant Morrison portrayed her scheming and manipulative villain during his run.

This version of Talia would essentially date rape Bruce in order to conceive a child, although Morrison would later admit that the reason he did that was because he misremembered the Son of the Demon storyline. Even if that part was never written, Talia is still portrayed as a villain during Morrison's run which later writers would continue. Fans of Talia hated how she was characterized but it does make sense for Damian's story.

Damian Wayne, the son of Bruce Wayne and Talia al Ghul, is portrayed as a violent and arrogant child who has no problem killing his opponents if he feels like it. Damien's early behavior reflects really poorly on Talia since anyone who raises a child to become a killer can't be considered a good person. Damian's character arc is about him learning to become a more heroic and selfless person like his father.

Damian has to choose between the path of heroism represented by his father or the path of villainy represented by his mother. His story wouldn't work if Talia was a good person since you would lose a lot of the narrative drama of Damian having to overcome his violent upbringing in order to become a better person. This kind of story only makes sense if his mother was at least somewhat evil in order to serve as a contrast to his father.