It is important to remember that Hamlet is a fictional character, one constructed by Shakespeare, who made him as complex and multifaceted as any character in literature.  Because there is considerable debate about his sanity vs. madness, we often forget how humane, how understanding of human nature he is also—in scene after scene Shakespeare shows Hamlet feeling, sympathizing, and caring for others, with a keen sense of others’ viewpoints and problems.  Some examples are his attitude toward the traveling players, his understanding of Ophelia’s feelings for him, his remembrances of Yorick, the court jester, and his distaste at the hypocrisy of Rosenkrantz and Guildenstern.  True, he is quite upset by his uncle’s and mother’s indifference to King Hamlet’s death, but those feelings are the drivers of the plot; if those were the total emotions of Hamlet’s character, we could accuse him of insensitivity and thoughtlessness, but the full-length portrait of the character belies this one-dimensional appraisal.  As for moral justification, the play revolves around that question, but his care to make sure he is not being deluded by the devil, his need for “ocular proof” of his uncle’s guilt, and his deep loathing of personal power or wealth is proof enough that in his mind he is morally justified (and in the eyes of centuries of audiences).