Slavery and liberty were the two most frequently used terms in the debate over freedom. How did they apply to the political rights of white property owners, but then mean something entirely different when referring to African-Americans held as property?
Slavery and liberty were used in very different ways when applied to the case of white people on the one hand and black slaves on the other. The basic idea behind this was that African Americans were simply not equal to whites and therefore slavery and liberty did not mean the same things to them.
White men were quick to denounce the British for, supposedly, trying to make them slaves. When they said this, they meant that the British government was trying, in some way, to deprive them of their freedom to act as they wished. They also meant the British government was trying to treat them as less than equal to British people. They felt that this was an infringement on their liberty and they, somewhat hyperbolically, labeled it as slavery.
With regard to African Americans, however, the white American men had no such worries. They “knew” that African Americans were not their equals just as they “knew” that white women were not their equals. Therefore, completely enslaving an African was not as bad as taking some liberty away from a white person. An African slave was not able (it was felt) to act as an equal to a white person. Therefore, taking liberty away from them was no worse than taking liberty from a child.