Maximus proves to be invincible in the arena, and news arrives that Commodus is planning a series of fights in the Coliseum. Proximo sees a potential payday. Maximus sees a chance to get within sword's length of the person who wrecked his life. Gladiator uses this mythic outline to bind together awesome action sequences and a dose of social commentary. There isn't much difference between the crowds cheering Maximus and fans of modern mayhem entertainment.
Money is the root of all violent exploitation then and now.
One of Maximus' endearing qualities is the way he resents the attention. It's insane to view these fights as fun. We like him enough to agree, then realize we're gawkers, too. Mano a mano, with much more than profit in the balance. Viewers shouldn't feel guilty watching Gladiator, but its impatience with trash-sports showmanship is unmistakable.