... an exam should be (moderately) difficult. Why bother having an exam if all the questions are so easy that all but the totally incompetent score highly? A good exam should show students what they have failed to master, as well as showing the instructor what they have succeeded in mastering.

Actually, those of you who are bright, ought to want difficult exams, the better to separate yourselves from your inferiors. Grade inflation harms the best students the most, because the good grades they earn are discounted when a course, an instructor, or a university gets a reputation for grading too easily. I should remark, however, that it hurts all students, because when you receive a grade higher than your performance merits, your instructor has either failed to exercise his/her professional judgement of your work, or has failed to deliver that judgement honestly.