Would you want your mentally disabled (adult) child to have children?

I saw a preview for a show on TV about adults with down syndrome (Born This Way, I think is what the name is). They were talking about getting/being married and were holding babies talking about becoming parents. It got me thinking about if I had a child that had down syndrome or another mental disability, would I want her/him to have children? I came to the conclusion that I would want my child to be as independent as possible and get married and have a fulfilling intimate relationship with their significant other but I don't know that I would be 100% comfortable with them having and being responsible for a child. What do you think? If you had a mentally disabled child would you want them to have children one day?