What is the place of mentally handicapped people in society?

What can they do to contribute to society and how should they live? I think most countries give them a meager social security that's barely enough to live on so if they don't have family to take care of them they inevitably become a part of the unhoused population.

Also even if they do have family to take care of them, what should they do with their lives? Should they contribute and be a part of society or should they do nothing but receive care? It seems to me being excluded from society is a sad existence but perhaps this is not the right way to look at things?