Oddly, this reminds me a bit of the controversy over Kurn's treatment on "Sons of Mogh" where some of the Tor commentators argued that Kurn needed therapy versus indulging his suicidal desires. I pointed out that I felt that Kurn wasn't mentally ill like many people with suicidal tendencies or depression. He was someone who was acting on a cultural taboo and the fact that he didn't want to live because ritual suicide was part of his people's reaction to dishonor. Which is different and not necessarily treatable (a patient has to want to get better and medication won't help Kurn).
Starfleet might view ANY desire to die as a mental illness, though.
Yes, I doubt you could have talked a Samurai from medieval time out of cutting his abdomen with a ritual knife (when the situation demanded it). If the prospect of a horrible death didn't deter him, nothing else would.