You can have conflict while "doing good for the sake of doing good". Case in point: Marche Radiuju. He spends the entire game just wanting to do what's right. Yet he's constantly conflicted because he just wants to stay in Ivalice (let's face it: who wouldn't). He's also thrown into conflict with his friends because they want to stay as well. Personal and interpersonal conflict. All because Marche wants to do what's right for no other reason than that it is right.

Done properly, this is almost always the case. It always leads to inner conflict, because what is right is rarely what is pleasant or pleasurable. Desire conflicts with morality. For a hero, morality wins that battle. For villains, desire triumphs (or they're just insane, but that's less fun).