A "hero" in modern fiction is a good person of uncanny prowess. A "bystander" or "Red Shirt" is an inconsequential nonentity character presumed to be "good." The "hero" is inclined to protect and avenge, whether reluctantly or wholeheartedly, the helpless "bystander." The "hero" cares about the expendable "Red Shirts" who accompany him into danger and is upset when they are expended.
A "villain" in fiction is an evil person as an antagonist. His indifference becomes malevolence and must be dealt with. Such a character may or may not employ minions. His thugs may vary in prowess between formidable elites and plentiful cannon-fodder. Regardless, those who serve him are an expendable resource in the pursuit of his agenda.
A "hero" is a "hero" when the lives of others are what he is fighting for. A "villain" is a "villain" when the lives of others are an expendable resource. Even if a hero is reluctant to help, if he helps, he is a hero. Even if a villain believes in the righteousness of his agenda, his willingness to sacrifice others vilifies him. Yes, a hero may lead other men to their deaths but only to save lives. A villain esteems notions more precious than the lives that serve him. Alas, good and evil are demonstrated beyond the subjective fancies of "right" or "wrong."