The problem of moral responsibility is intimately connected with the problem of free will, especially by modern "new compatibilists" who argue that free will may not exist but moral responsibility still does. Their arguments generally depend on obvious moral human behavior.
The first to use moral behavior to defend a compatibilist view of freedom was probably David Hume. Hume's "naturalism" was an empirical study of human nature. Although "Hume the Skeptic" thought that causality could not be proved, "Hume the Naturalist" was a confirmed determinist. Hume identified "moral sentiments" like praise and blame which arise from our sympathy with others. Hume's close friend Adam Smith wrote a fine essay on human sympathy called The Theory of Moral Sentiments.
The most important recent thinker to employ the moral sentiments in a defense of moral responsibility was Peter Strawson, who pointed to what he called our "reactive attitudes." Whether or not determinism is true, Strawson claimed, we would still feel guilt and pride in our own actions, and see Hume's moral sentiments such as praise and blame appropriate for others who were deserving of being thought responsible for their actions. Strawson called these persons "moral participants." We react to them with a "participant attitude." We would have no such feelings for persons obviously incapable of being responsible. These persons we treat objectively, analyzing the reasons for their moral failures. We react to them with an "objective attitude." For Strawson, the existence of "moral sentiments" and "reactive attitudes" is a sort of existence proof for moral responsibility, independent of the truth or falsity of determinism and free will. However, we regard the use of moral behavior as a proof of human freedom as an ethical fallacy. Even more important, we regard efforts by "naturalists" to use proofs of the non-existence of free will to deny moral responsibility equally fallacious. These naturalists deny free will to reach their noble goal of eliminating "retributivism," harmful and unproductive punishment of moral misbehavior. Naturalists say that agents do not "deserve" punishment. Since the agents' actions are determined, they can not be held morally responsible. Equating free will with moral responsibility, then using spurious arguments to deny free will, and thus to deny moral responsibility - in order to oppose punishment - is fine humanism, but poor philosophy, and terrible science.