If a husband thinks it's right or it's his right to beat his wife, he's living in an uncivilized society or he's ill-bred. Otherwise, he just has bad genes that cloud his moral sense and make him use brute force to give vent to his anger, frustration, etc.
Men happen to have more physical strength than women, so there are more cases of husbands beating wives. In an exceptional case, where the wife has more physical power, if she lacks moral sense and sensitivity, and at the same time has higher social position, she can potentially be a husband-beater too. In fact, there are such instances.
A spouse slapping the other on the spur of the moment is less serious, though it's still wrong. Chastening beating of a spouse is disgusting and should be punishable (and is punishable in India if the beaten spouse is a woman) by law. And a husband beating his wife to meet his demands is a serious crime.
I guess there are laws and cops in place in every civilized country to deal with wife-bashing hubbies.