The problem is that, apparently, abusing people wholesale is profitable.
Drug dealing is profitable. Chattel slavery was exceptionally profitable. To allow profitability to be our measure of permissibility is to sacrifice civil society at the altar of enterprising tyrants. Economics should never be a substitute for ethics.
it wasn't. Slave economies are exceptionally unprofitable and unproductive. To take the US as an example. Liquid wealth, i.e. capital, was vastly larger in the North than in the slave owning states, the industrial output of New York exceeded the entire Confederacy and it was that profitability, wealth and mechanized agricultural production that did them in.
Even Marx recognized this by the way, following feudalism capitalism was a progressive force, it was profit, productivity and surplus that enabled civil society, the north was more civil because it was rich and had unlocked modern forms of production. The problem of capitalism is not profit or lack of civil society.