I mean, of course I never want anyone to kill themselves, but with mental illness, that is exactly a thing that happens. How many veterans are killing themselves because of PTSD? It's a sad thing. and we should try helping them, but again, maiming yourself is never the answer.
Should we allow someone who thinks they're an orange to have a full skin tattoo that makes them orange and sit in a giant fruitbowl? Would we have to accept this person's trans-kingdom lifestyle?
Or hey. what about alien hand syndrome? Should we allow them to maim themselves so they feel that they are fixed?
Just because a mentally ill person believes something, doesn't make it right. And just because someone believes something is the correct course of action, doesn't mean it's the right thing to do.