I certainly think it is extreme language and I certainly didn't mean to imply that, as well-paid professionals, the majority of people on HN would be in a situation comparable to those truly in terrible situations: both overt slavery and what really amounts to actual slavery. I see it as purposely strong language used for emphasis.
I'm thinking more of the relationship between the employer and employee; ultimately you rent your time in exchange for money, which arguably for the majority of people is just enough to live their lives with some greater or lesser luxury, but ultimately doing unpleasant work which, though of course to some degree is necessary and serves society, is largely in place to make rich owners richer. A large mass of population simply acts within a confined system as 'slave wages' servicing the needs of the rich while only subsiding at a certain living standard.
I am contrasting this with those of us (and ultimately this probably applies to far fewer HN'ers than the general public) who find a way out, i.e. find value in our work beyond that of its means to provide us with an income, or in fact become one of the rich ourselves.
This is not a criticism of capitalism either, especially since I personally believe capitalism is the best means of distributing wealth, assuming controls are in place to prevent abuses.