What are some of the reasons teachers avoid discussions of social class? Why is this avoidance ultimately a disservice to students?

Teachers are always wary of offending or marginalizing students, even inadvertently. Social class of course leads to questions of ethnicity and pretty soon the teacher is on thin ice. These are emotionally charged topics that can cause grief in any socio-economic area. Also there should technically be equality in America but since the Regan/ Bush era, the middle class has steadily shrunk. Inequality in class has become the norm rather than the exception. This is a disservice because it is like taking an important piece of machinery when students are trying to find how an engine works. Avoiding topics of social class marginalizes all students to a sanitized sense of history which, of course, distorts the truth.