Yep. Some people really believe it doesn't exist.
Although, there has been a ton of research around dissociation since the turn of the century, and there is a growing acceptance and understanding of it now. Still some ways to go though I reckon.

I watched United States of Tara. There were some aspects I liked and some aspects I didn't like. Like switching so overtly... clothes and everything. Generally DID just isn't that.... florid.
I don't reckon a sitcom should be made about DID though. DID is intensely traumatic and painful. In USoT they did show some of the painful side which was 'good. But in general I would hate to see a sitcom made about DID as much as I would hate to see a sitcom based around a person with schizophrenia or bipolar disorder.