This is at least the second time I've heard someone say that the defibrillator implant shocks are so bad, they would rather be dead.
The most “usable” form of this would be to allow the patient to agree or disagree to the shock (maybe defaulting to agree if no response is given in time); this would place the agency in the hands of the patient and allow them to be mentally prepared. Missing that, at least a couple seconds of warning would be better than nothing.
(Disclaimer: I don’t know much about these devices or the latency requirements between detection of an abnormal condition and treatment; these suggestions only work if the heart can tolerate a few seconds of delay. It seems plausible since the detection itself is based on monitoring of heart rhythms over some period of time, but I am not an expert.)
Now the unpleasant experiences become something that I'm doing to myself, and that my animal brain in the moment has the power to prevent. Every intervention becomes a test of my willpower: I know that I need this, I know I don't want to do it in the moment... What's the harm in rolling the dice this one time, in exchange for avoiding just this one painful episode? The parallel that immediately comes to mind is "well, just this one cigarette won't kill me..."
I'd much, much rather pre-commit than have to face that aversive decision time after time and day after day. Knowing that my life is on the line if I'm caught in a moment of weakness. That calculus is much too important to me to leave to the whims of my reactive brain.