Patrick Rael on the 13th Amendment:

“First, the “loophole” argument imputes to its framers and judicial interpreters a conspiracy against intentions of full equality that the amendment never included in the first place. All the Thirteenth Amendment did was abolish slavery; it stood virtually moot on the meaning of freedom. This was by design. Antislavery legislators wanted a more comprehensive measure, but only by compromising on its vision would more conservative legislators let it pass. It took later amendments and laws to define freedom:  the Civil Rights Act of 1866 (civil rights), the Fourteenth Amendment of 1868 (citizenship), the Fifteenth Amendment of 1870 (voting rights), and others.

“Second, on its face, the language of the Thirteenth Amendment’s “exception clause” offers no mechanism to actively promote incarceration. Instead, its obvious purpose is to ensure that none mistake the prohibition on racial slavery for a prohibition on criminal incarceration. Given the novelty of emancipation at the phrase’s origin, that was not pointless:  surely the abolition of slavery should not mean that no one (black or white) could ever be incarcerated for crimes they committed, right?

“The exception clause alone did nothing to promote racial oppression. Search in vain for legal cases in which the clause was used to argue for the legality of any form of punishment. Instead, we see the opposite, as in in U.S. v. Ah Sou, C.C.A.9 (1905), wherein the court used the clause to argue against deporting a Chinese woman because it would have returned her to a state slavery in China. To justify their oppression, white supremacists used much more powerful and overt legal devices than slippery language in the Thirteenth Amendment. Jim Crow and mass incarceration would’ve happened with or without the exception clause…”

Read it all: Demystifying the 13th Amendment and Its Impact on Mass Incarceration