If he truly lacks a conscience then he is "criminally insane" and society locks those types of people up.
If you're just talking about an emotionally negative person, then both of the other commentors had good advice. Killing someone with kindness has a way of reinforcing good behavior and "mellowing out" negative people. Good deeds have a much greater impact than bad ones for a person's ego once you get the ball rolling. If you want to save the marriage, then avoid expressing negative emotions to your husband for a year, and absorb the negative emotions with a smile.
This should NOT however extent to physical abuse. The moment a woman is struck by a man, the man is no longer a man. In America, it's a cultural taboo. Leaving is absolutely the only answer, and it's not an easy decision to make. Absolutely the only answer. No question. One hand. Done. The first time is a red flag to the wife. The second time will be worse, and it only gets worse from there. There is no salvaging a physically abusive relationship, and the longer it goes on, the worse it is. To cross that line in a man's mind is a momentus step, even in a fit of rage. They will wish they could take back their actions, but the truth is that the line has been crossed, and it's easier to cross it again in the future.
Children might miss their father, but if physical abuse is in the scenario, then they will appreciate leaving that household too in time. Spanking a kid is the ultimate in punishment. A right cross to the jaw is absolutely 100% illegal and intolerable.