Chemistry students should learn research ethics from chemistry professors. Biology students should learn it from biologists. Scientists must not leave it to outsiders ethicists from the philosophy department, or the department of religious studies, or the Poynter Center to teach research ethics. Having outsiders do the only teaching on research ethics sends a clear message to science students that scientists do not care about research ethics, that it is a garbage course and a waste of their time. Please note that the above paragraph applies only when we are talking about the only course, or the required course, on research ethics.
Ethicists can serve a useful function.
They can teach elective courses, or they can teach units of required courses, or they can team teach with scientists. The important point here is that scientists have to be seen to be deeply concerned with these issues for the students to take them seriously. I think it is also true that people with training in ethics will tend not to teach research ethics very well, unless they also have experience or training in science. In the past this was a rare combination, but perhaps less so today. I suppose I should also say a word about what should be taught.