Actually antebellum blacks were allowed to vote least some Northern states unlike the South where no antebellum blacks were allowed to vote.The opposition to Lincoln and the Republican party in the South was universal. There was no need to inhibit their voters, because their numbers were insignificant.
To the everlasting shame of our nation, blacks were wholesale deprived of their civil rights, including the right to vote. It is true that they entered the country in a state of enslavement and their situation was accepted almost universally by Americans. However, that is another story for another thread.