Because Bane was a **** in the prison. A straight up *********. Talia "looked up to him" and probably loved him more than her father. She had major daddy issues. Her mom was ***** and murdered when she was like four and then this "protectah" comes along and "comforts" her.
Much older male "protectah"? I think it might have been more than just protecting someone who was born in a similar way that he was. There's also the fact that Talia looked like a little boi. I bet he convinced Talia that *** with oldermen is a good thing, that there's nothing wrong with it). I think he was also pretending to be her father.
That's why Ra's got mad and excommunicated him, he was a sick piece of ____! Not "too extreme".
I bet Ra's picked up on this and it made him sick to his stomach. So he ex-communicated Bane (because he reminded him of the prison and because he made his daughter mentally deranged. What was Ra's going to do with Talia? Ex-communicate her? His own daughter, his heir?
Plus, Talia hated Ra's, clearly. If Batman didn't kill Ra's, Talia and Bane would have. Talia and Bane were born and raised in prison, they were bat **** crazy.
To put it simply, Talia and Bane were ****ed up. They had a weird relationship from day one. Bane probably saw himself in her or some crap (let's face it, she looked like a little boy) and let loose. Talia was brain washed from the beginning living, what, 10 years in a hole in the ground?
"His only crime was that he loved me."
Oh yeah, I bet he did.
I know what you're thinking!