This is an invented objection. In reality, in classes of sufficient size, there is always a subset of students who work hard (or are extra smart, or whatever), a subset who is average, and a subset who slacks, or just doesn't understand the material well. The objection that there might be a mass class conspiracy to all score 40%, or that everyone in the class will be lazy, just doesn't make sense.
Who says it's a conspiracy? It's more a matter of culture. I have seen it happen: there's a trend in the class where the homework grades, on average, are high, but the exam grades are low, even though the material is mostly the same. This happens at reputable schools and at "low tier" schools.
