Yes yes the old 'work for me for pennies or don't and starve'. Not a valid argument - someone else will come along who needs labor and offer a better deal, the hypothetical worker can start his own business, or do contract work if there is enough demand.
There is at least one case when this argument is valid - when you're talking about state capitalism (rather than free market capitalism). In state capitalism, the capitalists pay the politicians for favors, which they redeem to tilt the labor market more in their favor. Minimum wage laws, licensing regulations, tax except employer health care... all of these things
sound good, but put up barriers to entry to the market. This means that the "exploited" employee must remain exploited, because it costs too much to start a competing business.