Schools should not eliminate "D" grades. For example, it could stop kids from INTERACTING with each other, because some kids don't like to hang out with kids with F grades. In addition, some kids aren't as smart as other kids, so just because they have a D that doesn't mean they aren't trying to do their best. It will take kids to a straight F, a D is better than having a F. Also, if they fail they can COMPENSATE by taking summer school and then they can still be having good grades.
In conclusion, I think that schools should NOT eliminate "D" grades, because having a D grade will INITIALLY encourage kids to try and get a better grade.