I get your point , Davy Crockett spent some of his younger years in indentured servitude working off a debt, a lot depends on where you draw the line. When the debt demands obedience and is constantly renewed or increases and is owed for generations it becomes a sceme of enslavement.
If a reasonable term of work allows the debt to be paid off it doesn't seem so bad, the more volentary and temporary it is, the less it is slavery.