As is putting them in a Hilton suite with an open tab and not letting them out until they are dead.
There are shades to this, and forced labor for prisoners is not necessarily a particularly dark shade. There are certain conventions against it in modern rules of war, not the least because working prisoners to death (with an emphasis on the death and little interest in whether the work gets done) has been a popular way to deal with POW hordes recently. But that's something of a fad: previously, there would have been little incentive to try such a slow and convoluted method of execution, when "wasting bullets" was not an issue yet and all killing was by straightforward means that were best, ahem, executed right off the bat. And of course having the prisoners work for you is logical, from which it then follows that keeping them fed well enough to achieve something with their work is logical. Folks outside the POW camps wouldn't necessarily have it any better.
With the Romulans, we again don't actually face any "cost of bullets" issues, but it's debatable whether manual labor really amounts to much in the 24th century. Romulans apparently have a long tradition of slavery, especially if we extend the "space Romans" analogy, but already because Remans; the tradition might support punitive slavery even if the labor was worth squat.
Then again, did we ever hear of a Romulan eagerness to execute prisoners? The female Commander laments how state criminals have to be subjected to this unpleasant procedure, but that's a fairly extreme case; Tomalak promised imprisonment as POWs only when Picard breached the Neutral Zone.
Timo Saloniemi
