I've had a friend go off psych meds for religious reasons (Christian Science) and nearly die (waxy catatonia from severe bipolar), so my objectivity is impaired. however:
my rule of thumb is that if the patient, after being returned to lucidity by meds, agrees in retrospect that meds were necessary, then it's the right call.
the other exception is if the person is at substantial risk of hurting others if unmedicated. then the violence of mandated medication is warranted.
barring that, if someone on psych meds wants to go back off them, I wouldn't prevent them from doing so.