I read up on the subject and, indeed, "Ben Hur" has created the myth of a concentration camp aboard a Roman ship. Sometimes slaves were used but in such cases they were promised freedom for good service. Of course, we have to consider the possibility that the creators of Star Trek or their historical knowledge had been influenced by "Ben Hur" starring Charlton Heston.
But the "galley penalty" became a form of punishment at the end of the 15th Century and the fictional nightmare we saw in "Ben Hur" became a reality for convicts during that time up until the 19th and 20th Century!
Spain adopted it early in the 16th Century, galley convicts were bought and sold like slaves. After I actually read the Hornblower novels my perception of the Klingons changed drastically. If Captain Kirk was Hornblower, then the Klingons were the Spaniards!!!
But whatever the case, the idea of a concentration camp aboard a ship is a concept the Klingons wouldn't mind to adopt, IMHO.