I think you're painting with too broad of a stroke here. I put myself through grad school working with developmentally disabled adults who were living in the community, but still needed a little extra help to make it. Some of them were the coolest, toughest, most awesome people I ever met and I'm proud to (still) count them among my friends.
That being said, there has to be a line drawn somewhere, and I'd probably draw it exactly where you did. "Are you you're own guardian? Can you sign a legal contract?"