He spent his life without a father and seeing his mother suffer so it's understandable that he wants to see Indu suffer
however
today I saw the goodness in Karan. In the preview when Sadhana is about to faint, he actually goes up to her and holds her from falling and is asking her what happened with concern.
He's not an evil character. He's actually a good guy trying to avenge his mother's pain. I hope the creatives turn him positive.