I do not agree with the main idea in this statement, which is that ethics classes in business schools are not worthwhile.
I do agree that students come to business school with their general sense of ethics already formed. A student who comes to business school with low ethical standards is not likely to suddenly be "reformed" by business ethics classes. However, even students with good ethics need to learn about ethics in the context of business. They may have learned good ethics, but they may not be aware of the ethical challenges that are specific to business.
So, while business schools cannot have a major impact on a person's ethical level in general, it can be important for exposing a person to the ethical dilemmas he or she will face in the business world.