What a fascinating question........and how few real answers!
Personally, I think a lot of the stigma surrounding mental illness stems from the way-back days, when demonic possession was pretty much the only reasonable explanation for it in the eyes of a society that was very primitive, especially when compared with ours. (And ours isn't a whole lot better when it comes to understanding the human brain.) The hallucinations, wild gesticulations, demented ramblings and other behaviors seen in psychosis were often 'treated' by brutalizing the 'possessed' individual, often in unspeakable ways.
Now we're a little bit kinder about how we manage mental illness, but still a long way from recognizing psychiatric patients as having the same rights as everyone else to seek and obtain good jobs, utilize their health insurance, even own firearms. An individual also does NOT give up his/her right to privacy when diagnosed with one of these disorders, although there is no shortage of employers and professional licensing boards which believe otherwise.
In the meantime, what we can do as healthcare providers---some of whom suffer from MI ourselves---is to educate each other as well as the public about what psychiatric illness actually is and isn't. Contrary to popular opinion, most of us are not wild-eyed maniacs with an Uzi and a voice telling us to kill the _____s (insert target of rage here); we're everyday folks who just happen to struggle with a brain disorder. People don't need to be scared of us, for we live next door to them, work alongside them, even make life-or-death decisions for them sometimes. In other words: "we" are "you".