This is far too unkind. Professors rarely make more than a pittance on their textbooks. They nearly always write textbooks because they need a textbook in a c

This is far too unkind. Professors rarely make more than a pittance on their textbooks. They nearly always write textbooks because they need a textbook in a certain area and there isn't an adequate one. It is an extremely demanding task with little payoff. The ethical error the professor has made is not in making money off the student (he's not) but in choosing a publisher which charges ridiculous prices without thinking about how this impacts on his own students.