DreamChaser said:
While a character can voluntarily forgo a save
Here is the flaw in your argument: the character does not "forgo a save"; the character intentionally fails the saving throw that they get.
Yes, the flat-footed person gets a Reflex saving throw. It is within this character's power to fail this saving throw intentionally.
Similarly, it is within a character's power to fail a Will saving throw. If you need a contrivance, let's say that some evil sorcerers have his sister hostage and threaten to kill her if he resists the
Detect Thoughts spell. Do you suggest that this brother has no choice but to make the roll, and if he succeeds, then be helpless as he witnesses his sister's death, which he was willing to avoid, but your ruling denied him?
Yes, the character also has the ability to try to attempt that saving throw, but allow the possibility that he can be convinced to do otherwise.
Once you allow the possibility that he can be bullied into failing the save, you open the door for someone to Bluff a target into willingly failing a save. "Ok, this is Arcane Healing and feels different from what Clerics can do, but it does the same thing. When you feel a force pressing aganist your psyche, relax and let the spell happen."
Someone with Knowledge (arcane) might recognize the lie, depending on the Bluff. Someone with Spellcraft might be able to recognize the spell being cast, understand that he has been hoodwinked, and then attempt the save. But someone who believes what is being told him has the ability to willingly fail the save.