If anarchism is a negative philosophy--and it is, at least in part--it needs to consider what it opposes and seeks to destroy.
What is the opposite to freedom but slavery?
Slavery has existed in many capacities throughout human history. What is given one name and codified as an institution has had many different expectations and regulation regimes, and though she may run the risk of sounding insensitive to split hairs about such Dire Matters, it is a wise historian who distinguishes Roman or Muslim slavery from that practiced in the American colonies and United States, or that seen in the Soviet gulag.
If we sidestep the historical hair splitting, however, we can see that slavery--at least so far as this writer is able to see--is not experienced as a discrete institution but of one piece with lived experience. It is the sum of the choices made by the individual and the social concerns that are part of all existence.
A slave contends with social forces that define him and threaten him with consequences of both his choices and random chance. A slave makes choices to the extent that she can and acts according to both external pressures and internal drives, urges, and desires.
A slave makes a choice to follow based on the same reason that we possess, although with different social training and different consequences.
On a very important level, there is a similarity between any free man we can imagine and the least free, as well. Anarchism, if it is of any use at all, must appeal and offer something to each.