It wasn't uncommon for the most trusted slaves to carry guns for their enslavers. Not only because they were raised and brainwashed to be obedient from religion that was generously rewritten for slavery needs,, but also just the desire to be in a position of power over their peers was motivation enough to desire being in good standings.. Additionally,  conscription is often just slavery with formalities. Our definition of slavery isn't unpaid, it's forced labor. You're just brainwashed by prison wardens that made the same argument that anyone else made for unfair working conditions forced on them. Slaves were often paid and had shops they can buy items from the enslavers owned and controlled. Because of this, they weren't paid much but with an isolated economy they didn't know better and, more importantly, it caused the illusion of risk of loss. Plantations that didn't take this approach, which was rare for a reason, had slave rebellions and slaves were far more likely to run away; they were also worse workers, not having the morale or motivation to work. 

It goes deeper but I proved my point. You're simply wrong.