I think I didn't frame my statement well. Although I don't make absolute claims about ethics, I tell the students that some practices are considered unethical by some people because of XYZ reasons. I leave up to the students to make up their mind because all of them are adults and many of them are actually much older than me. I have lived and worked in several countries around the world which has taught me that talking about ethics in an absolutist fashion is a terrible idea. Once I was teaching a bunch of internatioanl students predictive models to screen job candidates when the candidate pool is enormous to tackle manually. Some students felt that it was unethical to use algorithms to decide a human being's job prospects. I know it may sound weird to many folks on HN but people really have strong feelings about these issues on ethical grounds and it varies a lot from person to person and culture to culture.