The classroom is a microcosm of the external community, and how we conduct our classes says something about how we conceive of proper human relationships. In the classroom, students learn how to treat each other, in preparation for a life in a community of educated people. When we say what is important, we enter the realm of values. Let me elaborate on these fundamental ethical values in the context of teaching. We must treat all students fairly.
Nothing causes more dissatisfaction and anger than students' perceptions that the teacher is unfair.
We must observe stated deadlines for assignments uniformly, applying them to everyone equally. Any policy on accepting late submissions must state explicitly what conditions are allowed, such as an excuse letter from an omnipotent dean. Out of fairness, students must be evaluated on their performance, not on irrelevant factors such as race or gender. Examinations must be based on the content and skills covered in the course. To do otherwise would be unfair.