I think it comes down to social interaction really, even with other mammals like dogs a chihuahua can "dominate" a larger german shephard by having enough cockyness. yeah if the big dog doesn't want to yield it'd kill the smaller one no problem, but it wouldn't want to bother the risk of getting hurt over stupid shit. It the same way I could easily kill my female boss if she denies my a raise but it wouldn't be worth the social ramifications of rotting in prison. Even if there was no law, chances are she'd have a male relative bigger and stronger than I am that I'd want to avoid confrontation with.
I'd wager a trained fighter could kick a dozen average women's asses quite handedly if given enough time to prepare and not ambushed. Pic related.