in the movie Glory why did Lincoln offer the 54th an opportunity ti disband?

Answer 1

i don't remember if it was Lincoln, but the best i can remember is that if the black soldiers were captured fighting for the north they would be reverted back to slavery and if the white officers were captured they would be put to death, so they were offered the chance to leave without any questions, thus the opportunity to disband the 54th.

Answer 2

I havent seen he movie in years, but im gonna guess:
they hadnt won the war yet, so it wasnt clear that their rights, as black people would be absoulte, therefore, he thought it wasnt fair to make people fight for freedom they might never see.
again, im just guessing.