Republicans and Democrats Grade Differently - Thoughts

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I have a very unequal grade distribution, especially in my introductory economics courses.  I structure my tests so that it is very difficult to get 100s, and I typically get many scores below 50.  I curve my tests, but each semester I have a non-trivial percentage of students who will get a D+ or worse.  At my university, you then must retake the course if you are a business or economics major.

I view equal grading as unequal treatment, at least for a course like principles of microeconomics where assessment is straightforward.  If I were grade more equally, that would be extremely unfair to those who work hard to earn their Bs or As. 
Do I feel bad about the students who get a D+ or worse and have to retake the class?  Well, I don't feel good about it, but most who do poorly don't put in the required time and effort to succeed.  For those students, I don't lose any sleep over their earning a low grade.  They don't know the material, didn't work hard to learn it, and should be retaking the course.  There are some students who seem to work hard and still struggle to get results.  These cases are certainly rarer, but when it happens I am not happy.  I appreciate that economic thinking doesn't come easy to all students.  When one of these students comes in and puts in a sufficient amount of time studying, however, they usually do pass.

I guess this is roughly consistent with my views on income distribution as well.  Many who make lower incomes aren't earning their low incomes by accident.  Should we feel bad for the person who didn't work hard in high school, doesn't work hard now to improve him or herself, and has a job that pays slightly over the minimum wage?  I don't.  Note that I am not excited that a person is struggling, I simply don't get upset when a person's wages are commiserate with his/her effort. 

Further, some people make reasonable livings but made the choice to go into careers that pay less (teachers, artists, etc.) than other (perhaps less-appealing) careers that pay more (accountants, actuaries).  Unequal incomes here are a good thing, because if incomes were equal, we would have an imbalance in supply and demand in the various fields. 

Reading this report on grades - it makes sense to me.  Equality in incomes would mean inequality.  Equality in grading would mean inequality as well.

Note: The comment about grades by race is troubling.  Anyone who adjusts a grade upward or downward for a person because of his or her race should be fired.