In The Righteous Mind, Haidt draws support for his views from research by the philosopher Eric Schwitzgebel of the University of California, Riverside, and Joshua Rust of Stetson University. On a range of ethical issues, Schwitzgebel and Rust show, philosophy professors specializing in ethics behave no better than professors working in other areas of philosophy; nor are they more ethical than professors who don’t work in philosophy at all. If even professors working in ethics are no more ethical than their peers in other disciplines, doesn’t that support the belief that ethical reasoning is powerless to make people behave more ethically?This is a question that Socrates asked with some desperation, according to Plato; he seems to have died without answering it. Plato tried to answer it himself, but ended up with significant problems. In the Protagoras, for example, he has Socrates defending the weird proposition that ethics is a kind of knowledge but that it can't be taught (teachability being an ordinary characteristic of knowledge). He is debating Protagoras, who is defending the equally weird proposition that he can teach the virtues, but that they are not a kind of knowledge.
Perhaps. Yet, despite the evidence, I am not entirely convinced. I have had a lot of anecdotal evidence that my classes in practical ethics changed the lives of at least some students, and in quite fundamental ways. Some became vegetarian or vegan. Others began donating to help people in extreme poverty in low-income countries, and a few changed their career plans so that they could do more to make the world a better place.
Not to steal Tom's thunder, but Aristotle's ethics is the place where the question really gets answered. Aristotle bridges the gap by showing that virtue is taught by habituation. So it's not knowing what is right that constitutes 'teaching ethics,' but practicing doing what is right. In doing that, one develops a character that does right by habit, and thus crosses the gap that Socrates and Plato and Haidt and Singer are worrying about.
To practice what is right, it is helpful first to know what is right. Ethical theory has a place, even if it isn't the place Socrates and Plato hoped it would hold.