If someone starting a business works many hours themselves for $2/hour, and asks their spouse/children to chip in, and calls in favors from family and friends to get things going - then that's bootstrapping on cheap labor, but nobody in their right mind would call that 'slavery'. When starting a business when you have nothing, you have to be frugal, yet you can't do everything alone - that doesn't mean all ways you can get work done at below-market rates are sleazy or immoral.
That's exactly my point. A lot of the big companies today have at some point in their past exploited workers. Basically every manufacturing company started before WW2 or so.
Early factory workers where not exploited in terms of pay, they made more money than the average worker of their time period. Safty is a different story.