How can I get my brother to see how wrong he did his ex wife?

They were married for 15 yrs during that time he was abusive to her and cheated on her. I recently found out he racked up 53,000 in debit in her name credit cards. He finds it funny that she is poor and he had lots of money! He is old enough to know better he is 60 why must he joke about how poor she is and rub it in her face I told him Karma will get him! How can I make him stop? Another question is it justifiable to pick on the poor?