> That's outrageously ahistorical
First of all, there's nothing "ahistorical" about the simple fact that the South's economy was decimated after the abolition of slavery, and to this day the industry that utilized slavery the most continues to be weaker than elsewhere in the Union. That is your original allegation here: that slavery necessarily flourishes under a capitalist incentive structure. That's plainly untrue, because at the same time you had no slavery in the North, and its industrial economy outpaced that of the South (read: accumulation of capital, in your words).
You see this happening today as well: in countries where slavery is unfortunately still legal (Syria & Libya), they don't have any greater accumulation of capital or output than capitalist nations that do not have slavery (nearly every first world industrialized nation). On the other hand, nearly every single modern first world country, from Canada to Singapore to New Zealand to Switzerland to Sweden...all operate on capitalist systems where the majority of industries are privately owned, and operate for profit. They are also notably devoid of indentured/involuntary servitude while also enjoying some of the greatest accumulation of wealth and capital in recorded human history.
> The former slaves weren't suddenly "free" and unexploited in the US after the civil war. In many aspects they were still enslaved through various direct and indirect means.
Sure, nobody is arguing that people in the South were suddenly "free" after the abolition of slavery. You're absolutely correct that sharecropping and other practices essentially continued to ensnare black people in the South. The point is that this DID NOT translate to greater rewards in the capitalist incentive system. During Reconstruction, planters that exploited former "free" slaves LOST the agriculture race to the Great Plains, and the industrial race to the North.
> Furthermore your entire premise is false, even if we accept what you suggest is true, which is highly controversial, the result is not what we're talking about, but the incentive structure and what outcomes that will produce. Of course people searching to accumulate capital will endorse and proliferate low labour costs if it's possible and currently acceptable.
There is nothing unacceptable about "low labor costs" in a society with robust social safety nets. Countries like Switzerland that have close to 0 poverty, the highest median wealth, and among the highest standards of living in the world also see variation in labor costs between a janitor and a doctor, or a fast food cashier and a civil engineer. Not all labor is equal in value, and the capitalist incentive structure prices labor as a function of the value that it creates for others. If your argument is that this is somehow tantamount to chattel slavery, then it's you who is regurgitating propaganda.