I would stand up for the people he's talking about. Don't necessarily tell him he's wrong because that'll just start something new. Let him see the good side of the people he's talking about. Try to change the subject when he talks about people. Remember, if people know that he talks about people and they see that he's hanging out with you that could possibly give you a bad rep. Try to stay away from what he's saying whether it's true or not. Good luck