...All in one!
Before you read this, know that it's mostly a joke, but between you and me... It would probably work quite well. I think it makes a point about human nature, too.
So, the population of the world is growing. Prisons are becoming over crowded. Reality TV is s**t.
I can sort all these problems out at once! How?
Take the criminals who've been convicted of a major crime (murder, rape, etc), and put them on a TV show. It will be very cheap to set up since all you need to do is feed the prison CCTV to a studio. That's right, a reality TV show in prison. Like Big Brother but with criminals.
The twist, though, is that deadly "challenges" and "obstacles" will be put in the cells. I'm thinking venomous snakes, hidden traps, etc.
The game is simple: who will survive the longest without being killed by a snake or by another prisoner? No guards or anything, just let them run wild and kill each other.
You know what, forget what I said before about it probably working. This would work, 100%. Why? Because humans are humans, and even though we like to think we've become more civilised over the years, we just haven't. So we will get the same enjoyment from this as we did from public hangings. Humans enjoy watching others suffer.
Plus, we know the prisoners going mad thing will work because of the Stanford Prison Experiment. Of course, in that experiment there were guards who automatically had authority, but if you just leave the prisoners to their own devices they'll form a hierarchy anyway, like in Lord of the Flies.
Hell, you could even introduce some sort of phone-in voting system where you vote for someone you want to be killed. That'd make it profitable too, and it'll have the hype factor since everyone will want to know who wins.
Of course, possible moral questions could be raised, but this is being done to convicted criminals anyway. Surely they deserve it?
Just a random thought.