There's many aspects of slavery that are weird. In a free labor system, you have carrots that you hold out to employees and if they don't do what you want, you reduce or eliminate them. How do you get those people to work? Well, that's where you move from carrots to sticks, literally in some cases. And then an entire system devoted to preventing any sort of insurrection, rebellion, rising up or resistance. We americans liked to poke fun at the gastapo question but didn't acknowledge there were lots of people that had to show their trouble or be beaten or worse.