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When you willingly work excessive hours under an unfair master, you devalue both your own time and everyone else's in your position. It's not just about you; labor is a market, and the price is set by supply and demand. An excessively supply - i.e., people working more than they ought - effectively drops the cost. So, if your boss can get you to do two people's work, they don't need to hire two people - and that's either someone out of work or, in your case, a parasite of a boss who does nothing.
Overall, each person who allows themself to be exploited just makes life harder both for themselves and everyone else.