So instead they just hand you a B and say "Have fun?" How does that benefit the students? Or to a greater extent, society? You're essentially rewarding mediocrity. The reason you have tiered classes is because one class builds off the knowledge gained from the previous. If you get handed a passing grade, how are you suppose to understand future courses that build on that material? Now granted, the only professors I've had that do curve to a C generally teach upper level science courses where being an "ABOVE AVERAGE" student is important. These classes are hard and DEMAND time and effort. That said, I've never had a professor curve down, because that means the professor is punishing students for his/her fault (like writing a test that wasn't hard enough). In addition, courses like that, generally require a C to pass, or a B if it's a core class for your major, in which case you better damn well know your material.