Tarrlok revealed that he was Amon's brother and that he suffered from his bloodbending training with his father in his childhood. He says he hated any minute of it and even disobeyed his father when he was tasked to bloodbend his brother. He also says he could not take it anymore to torture innocent animals.
So why did he go after the dream of his father? Was this even an "avenge me" situation or did he do that for his own goals