I always get rather nervous when I see posts like this. Things like this obviously happen. However - statistically - people with mental illness are no more likely to commit violence than anybody else.
See http://psychcentral.com/archives/violence.htm for example.
When people with mental illness are violent it's usually for the same reason everybody else is. It's usually aimed at family when it does occur - not the world in general.
The story that gets portrayed in the media of mentally ill people being a major danger to the general public is just that - a story. The facts don't back it up.
And those with mental illness have to deal with the bigotry and prejudice that results from this story.