It has been my experience that the following is not true.

"but seldom out of their own free will."

Slaves decide to be slaves for the convenience of not taking a look at themselves for the express purpose of self improvement. People are essentially trading there liberty and freedom for not being responsible. It is just a law of nature that if you won't be responsible someone else will for the prophet of your sweat equity.

This is why I spend most of my post on education. For if there be one slave in the world we all suffer the consequences. It just so happens that nature itself creates the conditions. Slavery is actually a illusion, because there are consequences for inaction or action and you and I have made the choice by the actions or inaction of our lives. So have we all.