Why does M&M get angry at Mark after he helps to rescue him from Curly Shepard?

After saving M&M from being beaten up, Mark is full of adrenaline and wants to keep fighting. He sees a black man nearby and asks Bryon if he wants to jump him. M&M hears this and gets upset with Mark. M&M states that Curly wanted to beat him up because he was different, and now Mark wants to beat up the black man for the same reason.