Hi, i don't think there is necessarily any link between mental illness and suicide any more than any other (severe) health condition is linked with suicide. The difference is that from the day a person starts to develop mental illness they get the cold shoulder and cruelty (to whatever degree - sometimes severe cruelty, such as the mental health system dishes out) - they never get anything else. Any other health condition attracts sympathy or empathy, one would hope, and I think that's generally true.
the causes of stigma tend to be misinformation and ignorance. of course, it doesn't help that the 'professionals' lump psychopaths and sociopaths in with all the nice, normal decent people with mental illnesses. and it doesn't help that most psychopaths try to pass themselves off as having paranoid schizophrenia in order to get lesser penalties for the crimes they commit, and the psychiatrists mostly believe them.