Teaching opposing views depends on what part of the Holocaust the teacher wants to focus.
I suppose you are correct in a very technical, abstract sense, in that focusing away from any negative aspects of the Holocaust is, in a way, a shift in focus away from parts of the Holocaust - specifically, it is a shift away from any parts that would place that event in a historical context, and a delibate focus away from its material reality and towards a collection of meaningless abstractions, as in the manner of your suggestion to focus on its "efficiency", steadfastly refusing to look at that alleged "efficiency" in context.
In the classic technocratic mistake of argueing in circles of the "how", we, of course, completely miss the question of "why" - what would be the purpose of treating horrid historical atrocities in that manner? It strikes me as rather peculiar that you never cleared that up before you went full steam ahead with the question of methodology.
Why don't people have this reaction to say slavery... the point is the same.
Slavery didn't form a part of my country's past that's still within living memory. But I recognize that there are many who are so far removed from atrocities that they can treat them in a distant, jocular manner or as subject of dispassionate, abstract debate on the same level as debating the value of different flavors of ice cream.
I also think you are sorely mistaken when you presume that nobody has strong reactions to slavery, because I have certainly observed people react with disgust at the suggestion that there would be positive aspects to human bondage; which suggests that they probably weren't as far removed emotionally, and so probably did not feel as lighthearted on the subject as others who might be less burdened by the reality of atrocity...
Opinions in an education environment is fine. Just as one talks about suicide and even can debate on why some think it's justifiable and others not so much. But it's broached in a way that doesn't promote suicide.
I don't know what school you went to, but I strongly doubt that your curriculum included a debate on the pros and cons of suicide. I know that mine didn't. As a teacher, I would strongly refrain from broaching a subject in this manner, and your position in this matter betrays a frankly devastating ignorance on how to teach sensitive subjects to teenagers.