Let's just say this up front: Mr. Murdstone is one mean dude. He's a vicious tyrant who gets his jollies from tormenting weak, defenseless women under the guise of "improving" them or "disciplining" them. Mr. Murdstone flatters silly Mrs. Copperfield into marrying him. Then, as soon as she does, Mr. Murdstone (in Miss Betsey's words) becomes "a tyrant to the simple Baby, and [he breaks] her heart" (14.135). And Mr. Murdstone is so committed to this pattern of behavior that, once he gets over Mrs. Copperfield's death, he marries another young woman and breaks her spirit.
What virtuous characters like Ham Peggotty have is precisely what Mr. Murdstone lacks: sympathy. He has no sympathy for David when Mrs. Copperfield dies. He can scarcely bear to look at David because he feels guilty for his own treatment of Mrs. Copperfield before her death. So, instead of comforting David, who has just lost his mother, Mr. Murdstone sends David away to a factory to rot until David runs away and determines his own destiny. Mr. Murdstone is an exaggerated villain, about as maddening and loathsome a character as you'll find anywhere in literature.
But Dickens is not willing to let Mr. Murdstone go without any psychological depth: he's not just a monster (though he is a monster, don't get us wrong). The thing is, there is a fascinating moment in the novel when Mrs. Copperfield timidly protests David being whipped. Miss Murdstone answers back that her brother has been whipped loads of times. Mrs. Copperfield asks if it did Mr. Murdstone any good to be whipped like that. And Mr. Murdstone butts in: "Do you think it did [me] harm?" (4.95).
Obviously, Mr. Murdstone expects that the answer will be no, that whipping hasn't done Mr. Murdstone any long term harm. But our answer is, heck yeah, it did him harm! There seems to be some implication that Mr. Murdstone was himself brutalized as a boy. As the object of sternness and cruelty himself, Mr. Murdstone seems doomed to repeat these abuses on David. Sure, this doesn't excuse Mr. Murdstone's behavior, but Dickens seems to be hinting at an explanation for what has made him this way. (For another intriguing explanation of evil, check out our thoughts on Uriah Heep.)
Something else we have to give Mr. Murdstone props for: in his truly messed up way, he does seem to love Mrs. Copperfield. Miss Murdstone seems to be entirely cold and totally inflexible. She is truly a sadist, perhaps because she has so little power of her own. But when Mrs. Copperfield and her infant son die, Mr. Murdstone frets in painful silence, unable to speak even to his beloved sister (9.78). And Mr. Murdstone does feel enough guilt over his treatment of David's mother that he cannot bear the sight of David himself. Mr. Murdstone has feelings – stunted, awful feelings – he just doesn't let them guide his behavior towards other people.