Having mental illness is hell; not being able to talk about it is really cruel. Old, old fears and misconceptions that go waaaay back. Times when the mentally ill were locked up for life in some dark institution, left alone. Scares people. Afraid they're the ones who will be 'crazy' and abandoned. The way to stop the stigma is to bring mental illness out into the light. Attend gatherings (like the ones NAMI has), meet with others who are mentally ill. There's strength in numbers. If you're really courageous and it's safe, tell people about your mental illness calmly, as though you were discussing any average thing about yourself. The more people open up, the less stigma there will eventually be.