Forcing to work (free in the original quote) is the deprivation of this right. So what is the difference?

The difference in the amount of rights you are losing. Chicken potatoes and other mandatory work - one level. Working house, debt or just prison is another level. Army - third level (you may be legally forced to die). The state of slavery is the last, deepest level. If you mix it all into one phenomenon by one formal feature, I find it superficial, although for some, property is theft. In general, a strong work on this subject – Michel Foucault’s Birth of the Prison, there the social mechanics of coercion is thoroughly uncovered.