Exile, Execute, Incarcerate, Enslave... or what?

How do you handle an undesirable prisoner? (In fiction, specifically in alien romance fiction.)

In Lexx (http://en.wikipedia.org/wiki/Lexx), criminals' organs were harvested on a mechanized assembly line without the benefit of anaesthetics or any other drugs (of course!) and the remains were utilized as organic fuel (food) for the dragonfly-like, organic spaceship, Lexx.

Some victors would play with their prisoners, or with their body parts. For instance, on the FIFA site, http://www.fifa.com/classicfootball/history/game/historygame2.html it claims

"One theory is that the game is Anglo-Saxon in origin. In both Kingston-on-Thames and Chester, local legend has it the game was played there for the first time with the severed head of a vanquished Danish prince."

That appears to be an isolated, and not particularly efficient solution to the problem. Possibly the Orcs use of
severed heads as cannonballs (in LOTR) was more practical, and also more demoralizing to the enemy.

Ancient Romans would either enslave prisoners, or make gladiators of them, or assimilate them. In one of the Star Wars Prequels (Clone Wars?) there were gladiator pits, but inconvenient prisoners were intended for amusing execution, rather than being given a fighting chance.

At one time, the British exiled prisoners, shipping them off to "the colonies" or "the Antipodes", for instance, which has always struck me as rather unfair to the native peoples. One of Anne McCaffrey's series (Freedom's Landing) used captives as experimental colonists, to demonstrate whether or not a new world was suitable for annexation.

At other times, the British housed prisoners in unseaworthy "hulks", or prison ships. Americans used islands... and still do. Russians sent prisoners off to Siberia. Captain Kirk was sent to an isolated prison camp to work in the mines on the frozen asteroid Rura Penthe, in The Undiscovered Country.

In theory, someone imprisoned on their own planet has a chance of escape without outside help. Space is an insuperable barrier to escape, unless one has rescuers, or magical time-travel abilities, or is able to overpower the guards and steal a space shuttle or stow away on a supply ship.

Riddick (http://en.wikipedia.org/wiki/Riddick ) is a good example of a science fiction convict who makes good --sort of-- without the benefit of organized rehabilitation.

Assuming that one wanted to write an alien romance about someone who had escaped from long term incarceration, would it also be a Revenge story, such as The Count of Monte Christo? Otherwise, perhaps they could have done their time, and been released legally. Or they could be pardoned, rightly or wrongly.

Here is an interesting comparison of slavery versus imprisonment: http://www.stalags.com/ and also an explanation of post traumatic stress disorder. It seems to me that being wrongly convicted, and forced to work in prison would combine the worst of both situations.

Here is an article about the need to rehabilitate prisoners.
http://www.pennlive.com/midstate/index.ssf/2011/05/john_wetzel_pa_secretary_of_co.html

That does not account for political prisoners. In a Machaivellian world, one might wish to turn prisoners into Manchurian candidates, or otherwise mess with their minds to make them useful. But, if they are celebrities, and recognizable, what does one do?

"The Man In The Iron Mask" would not be a plausible plot line unless one's world was a world of superstition, and one believed that to kill a king (for instance) would damn one's immortal soul, or set a precedent that might lead to one's own execution.

Honestly, if one were evil enough to frame an innocent man --or arbitrarily throw a rival into the science fiction equivalent of an oubliette-- is there any plausible reason why one would not kill them?