Yes, it is fair that diplomas are worth 50% of a grade, because schools and employers can come up with any evaluation system that they want to. People can choose what kind of education they want to obtain, with whatever kind of grading system they think is fair to them. Diplomas are important.
Diplomas are hard even if a kid gets 75% in a class getting a hard diploma and not doing great on it drastically drops a persons mark! Yes it is important to retain and test the knowledge students learn but making a test 50% of their overall mark? Why? When you put importance on that one test does it even matter what they did through out that year? Testing is important but making a person fail a class because of one mark on one huge test at the end of the year.. This can wreck someone's future.. The difference between getting the good mark or barely passing.
I believe that diplomas just aren't worth anything at this time, even if it counts for 50% of your grade, what should really matter is what knowledge you have gained to get diplomas, anyone can get diplomas and not really know anything about what they learned. It should be given that after they completed something that was worth 50% of their grade.