To decide what I should think about abortion, for example, I would have to take a survey of American society and then conform my beliefs to whatever society accepts. But no one ever tries to decide an ethical issue by doing a survey. Further, the lack of social consensus on many issues makes it impossible to equate ethics with whatever society accepts. Some people accept abortion but many others do not. If being ethical were doing whatever society accepts, one would have to find an agreement on issues which does not, in fact, exist.
Ethics is two things.
First, ethics refers to well based standards of right and wrong that prescribe what humans ought to do, usually in terms of rights, obligations, benefits to society, fairness, or specific virtues. Ethics, for example, refers to those standards that impose the reasonable obligations to refrain from rape, stealing, murder, assault, slander, and fraud. Ethical standards also include those that enjoin virtues of honesty, compassion, and loyalty. And, ethical standards include standards relating to rights, such as the right to life, the right to freedom from injury, and the right to privacy. Such standards are adequate standards of ethics because they are supported by consistent and well founded reasons.