This is a textbook thought experiment in utilitarianism, carried to its logical conclusion. Kill one person, save eight. We might not like it, we might consider it abhorrent, it might contravene international human rights law, but we can't argue that it's senseless.
It's not really utilitarianism at all. There is nothing in utilitarianism that says round up some undesirable group and kill them so a few wealthy people might get organs so they can live. The greatest good for the greatest number of people. What is the consequence of these actions, well first murder. That leads to no happiness for the murdered, their families and loved ones. The people receiving the results of that…
If those victims were to die anyway, it does become somewhat of an utilitarian problem.
And if it is, the gaming issue that would bias decisions towards executing the prisoners instead of "lighter" sentences due to the "gains", which creates a vicious feedback loop ; and the fact that overall the gains in that system are not just people surviving, but also captors getting rich ; should point clearly to the vice and undefiable corruption that make it undeniably unethical.
That and the fact that a regular human with any ounce of love or humanity in its blood should feel how wrong and disgusting this all is