I don't want to have combative arguments in a graduate course
What would you say or do?
I think the best way to deal with it is to discuss the situation rationally.
It's fine not to want to get into arguments at school. It's totally understandable. You should talk rationally. I think it might also be worth keeping an open mind you may learn something from other people.
I'm not a victim. I can confront him or just drop the subject.
You don't need to allow yourself to be victimized. Instead I think it might be good to stand up for yourself and study hard to make sure your points are valid.