[nailer]

> the use of force inherent in slavery.

The article in question mentions agreeing to willing slavery, i.e. without the use of force:

> Once we get this far, we are almost all the way to Carlyle on slavery. We have not agreed that a man can be born a slave, but we agree that he can sell himself into slavery. That is: he can sign a contract with a master in which the slave agrees unconditionally to obey and work for the master, and the master agrees unconditionally to protect and support the slave.