This is necessary since in the real world throughout history, all human beings justify their deeds as the right thing and the opponent's as villainous.
But while 18th and 19th-century women guilty of treasonable crimes were still seen as villains, increasingly, the cause of their descent was ascribed to villainous men.
More powerful villains strive to contest for greater goals like world domination and/or universal acclaim (from the public and their villainous peers).