Those instigating the punishment quite clearly do not intend for it to go beyond the cessation of all function in the body.

This is not clear to me. It could just as easily be that the intent is for the person's memories to be completely erased from the body in order that the person would not be able to return to life and commit the same crimes again. Otherwise it would not be as much of a punishment.

Prohibiting cryonics is not the default state, the status quo. It would be an additional punishment.

From a legal rights standpoint perhaps this is correct. But from an actual action-taken standpoint, it isn't. The status quo for a condemned criminal is to die and rot. If condemned criminals started doing cryonics, it would be a disruption in this pattern. Those in favor of the status quo of condemned criminals dying and rotting would be against this and in favor of regulating cryonics to prevent it.