It might be rational to do so under extreme enough circumstances. For example, if a loved one had to take pills every day to stay alive and had a tendency to accidentally forget them (or to believe new-agers who told them that the pills were just a Big Pharma conspiracy), it would be neither madness nor tyranny to do nearly anything to prevent that from happening.

The question is: to what degree is failing to sign up for cryonics like suicide by negligence?