Like others have said, the stigma is there because when do you ever hear about schizophrenic people? When one of them has done something violent.

My cousin has schizophrenia and sadly he does have the violent streak. As long as he's medicated he is okay, but he was never able to work due to issues with people having authority. He is now in his 60s and hasn't had any trouble since being diagnosed and medicated, and is a great person.

It is the same with all mental illness. If you're "bipolar" you're making an excuse because everyone can be happy one day then sad the next. Or if you're depressed you just need to "suck it up." And of course ADD is obviously an excuse for letting your kids run wild... It is unfortunate but we all suffer under the stigmas of society.