If a person is denied a right to vote, he knows then and there he is being disenfranchised. They can step forward and show conclusively that a problem exists.
If my vote is being undermined by fraud, I have no way of knowing that I am being disenfranchised. nobody can step forward and prove the problem exists, that doesn't mean the problem isn't there.
as a scientifically minded individual, I choose the system of knowing over the system of not knowing 10 times out of 10