There appear to be some missing relevant items and/or inaccuracies in the discussion of Henry Laurens.
He was not just a wealthy rice planter. He became one of the wealthiest men in North America primarily by being a partner in the continent’s largest slave importing and trading firm.
Conditions in the Tower of London were not necessarily appalling. They varied from luxurious to horrific, depending on what the prisoner could afford and the treatment specified by the government. Laurens was not treated particularly harshly.
He was certainly treated much better than American prisoners in British hands in America, where the death rate (over 1/3) considerably exceeded that at Andersonville during our civil war and of American POWs in Japanese hands during WWII. It was roughly equivalent to that of Russians taken prisoner by the Nazis. This is an element of American history that’s largely been forgotten.
I can find no evidence Laurens ever freed his slaves, except perhaps one or two of his hundreds. He expressed dislike of the institution and a theoretical desire to get rid of it someday. But then so did almost all southerners of the day.
John Laurens, however, was indeed an outspoken foe of slavery.
I see conflicting accounts of whether he freed his slaves or not.
This account is from the South Carolina National Heritage Corridor established by congress.
http://www.scnhc.org/story/a-revolutionary-profile-henry-laurens
“Henry buried his son on the plantation, and after the war he freed all of his (then 260) slaves.”
But I also see...
https://networks.h-net.org/node/950/discussions/63282/inquiry-did-henry-laurens-free-his-slaves-after-american-revolution
In volume sixteen of the Papers of Henry Laurens, editors David R. Chesnutt and C. James Taylor has mentioned how Laurens dealt with his slaves in detail. “At his death,” according to the editors, “[Laurens freed but one slave]. His stated policy never to sell a slave for profit and to purchase one only to unite a family appears to be supported by the documents” (xxi).