Completely selfish in most circustances. But one is free to be selfish. In that case I imagine that kharma would dictate that at some point the suicidist would be provided the same feelings of loss, abandonment and fear that he caused others by his suicide.
Euthanizing a psychotic person as described is murder, unless he is killed in the process of doing damage and cannot be restrained. From study and secondhand experience, the extreme psychotic is in no distress and not suffering, all appearances to the contrary.