Yeah, no.
The lyric is alluding to the fact that the country's foundation was built on 100s of years of free labor.
The practice of exporting worthless printed paper in exchange for valuable labor intensive goods is also what that lyric is pointing to.
American slavery, a model that has evolved and now encompasses much of the globe.
Keeping a large % of the world and "undesirable" domestic population poor, at gun point if necessary, is in America's national economic interest.
Such as your opinion.
I don't think slavery would have been abolished without the industrial revolution.
That is most certainly not the usual interpretation of free labor.
The overwhelming majority of slaves in the US were field hands in plantations growing cash crops. How exactly did rudimentary agricultural mechanization around the time of the American Civil War in any way precipitate abolition?
You're right, it's not profitable for the government (although it probably is profitable for some private prisons who also receive money from the government).
"The U.S. spends $81 billion a year on mass incarceration, according to the Bureau of Justice Statistics, and that figure might be an underestimate."[1]
1: https://www.pbs.org/newshour/economy/the-u-s-spends-billions...
Cause free labor's the cornerstone of US economics
Cause slavery was abolished, unless you are in prison
You think I am bullshittin? Then read the 13th Amendment
Involuntary servitude and slavery it prohibits
That's why they givin' drug offenders time in double digits
- Killer Mike, Reagan