That would indeed be interesting, particularly because it would be a good test of how seriously people take cryonics when they're not motivated to deny the possibility of its success (to explain why they don't want to sign up, or why it wouldn't have been any use in saving the life of a loved one, etc.) — we'd see how many of them seemed to be seriously worried about the death row convicts coming back someday.

I think you have just suggested an excellent persuasion tactic. I can't think of a better way to convince people they want something than by having them see it as a privilege that a deplored group don't deserve.