This is a good question... If you see it as punishment of an evil person, it follows that they should be denied cryonics for the same reason they are being killed.
But if you believe in rehabilitation, thinking of the criminal behavior as the result of a mental illness, cryonics is a good thing because they are being sent forward to a time when their mental disease can be cured.
It would be interesting to see what would happen from a political standpoint if a death row inmate were to express a wish for cryonics. Has anyone tried sending literature on cryonics to condemned criminals?
The main point of punishment is to deter crime, rehabilitation is secondary. One to think of this using TDT is that the point of punishment is to acausally prevent crime. I discussed this in a slightly different context here.
As to whether a criminal should be allowed to sign up for cryonics, that depends on what the appropriate level of punishment for his crime is. After all, we assign some criminals 10 years in jail, others life, and execute still others.
As the question of mental illness, as Yvain points out in Diseased thinking: dissolving questions a...
If someone is sentenced to life in prison or the death penalty, should they also be prohibited from signing up for cryonics? Specifically, I'm referring to people like these: http://en.wikipedia.org/wiki/List_of_United_States_death_row_inmates
I am not talking about providing it for them, just allowing them to sign up for it provided they can somehow get enough money together and allowing a response team into the prison to retrieve the body after the prisoner has died or been executed by lethal injection. I think they should be allowed access to cryonics, because we don't know enough yet about the brain to determine how much of their criminal behavior is due to mental illness/disorder and how much is due to free will. It may be possible to diagnose and cure people like Jeffrey Dahmer in the future before they commit any crimes, or to cure those already in prison such that they won't commit any more crimes.
As cryonics gets more and more popular, this will become an issue, especially when the first death row inmate wants to sign up for it.