I'd like to dichotomize here between the two definitions of freedom and slavery that you've placed. The author primarily speaks of slavery in terms of one willingly accepting dogma and shackling oneself to some form of restriction that keeps them from performing other things. Steady banking job at the cost of keeping you away from wife and family? Get to work 8am, come home 8pm for the sake of financial security? That is slavery, but amusingly in this piece, it is the freedom of choice that one has that was used to willingly revoke the freedom of the mind to explore alternative options. Nobody will argue that the camps of North Korea is "security", but definitely will argue "slavery", but this is due to an external entity enforcing its will upon the individual to deprive them of their freedom.

Excuse me for indulging in some nitpicking, but I do believe that this piece primarily spoke of freedom in the context of actively removing internal restraints from your mind and being "free" as it was, to explore options and alternatives without some form of restriction weighing you down. Slavery being discussed in the sense of it being one where one willingly accepts some dogma in order to bear the weight of something that they have chosen to do (i.e. the repetitive lie of the banker as he tells himself that his financial security is more important than loving his wife and children).