Reading your linked article, it's clear that this was viewed as absolute quackery even back then, and is about as conflict-of-interesty as you can get: commissioned by Louisiana at the height of the Civil War, and proposed by a doctor who served in the Confederate Army [1]. His suggested treatment for Drapetomania was "whipping the devil out of them".
[1]: https://en.wikipedia.org/wiki/Samuel_A._Cartwright