Why do people obey orders that are unjust or immoral? Are they responsible for their
actions?

In everyday situations, people obey orders because they want to get rewards, because they want to avoid the negative consequences of disobeying, and because they believe an authority is legitimate. ... People justify their behavior by assigning responsibility to the authority rather than themselves.

regarding the law, the 15th amendment was specifically designed thinking in the rights of black free men.

even though ratified on february 3, 1870, the promise of the 15th amendment would not be fully applied for a long time.poll taxes and literacy tests would allow southern states disenfranchise african americans. only in 1965 the voting rights for african americans would be actually able to vote in the south.

in 1965, president johnson signed the voting rights act, which aimed to overcome legal barriers that prevented african americans from voting as it was guaranteed by the 15th amendment to the u.s. constitution.