Because from an evolutionary perspective, Women A) Take priority over men, because they are capable of reproducing B) Have the power of Mate selection to offset the weaker position they take on from the more aggressive men. When either gender abuses its evolutionary strength, it is perceived as unsustainable, and therefore highly immoral. This is why men abusing physical dominance through violence is considered so unacceptable, and why women abusing Mate Selection through cheating is seen as much worse compared to men, who are just programmed to screw anything that moves. Both double standards have an evolutionary basis. Also, C) Violence and control being visited on a female from members of your, "Tribe" would, from the perspective of evolution, be a frequent precursor to Rape. Evolution selects for individuals who are extremely aggressive against perpetrators of rape, as it takes away a woman's power of mate selection, and cuckolds the male. Basically, domestic violence implies rape in our lizard brain, and males must disapprove strongly of rape, for the express purpose of avoiding being forced to raise another persons child.
This is why I laugh when people talk about evolution like its some kind of benevolent force. Evolution is a very real thing. Its also cruel, evil, and dumb as shit. It would be difficult to design a more cruel, or less efficient process.