How the US Army Helped Freed People During the War

The US army helped liberate so many enslaved people and by the war second year had started to form black units. Many freed people were eager to fight for abolition in the sea islands off the coast of South Carolina. But as you referenced just a few minutes back the army could also be quite brutal in in places forcibly impressing freed men into being soldiers or forcing black people to labor in conditions that resembled slavery. What explains these varied approaches by the US army towards freed people?