Did you see the footnotes at the link? The parents understand that most people have no malicious intent. They just want people to understand how their actions affect others. With most people, that’s all that’s necessary. It is the rare individual who has true malice toward disabled children. Most people just don’t realize how isolating disabilities can be, and how hurtful it can be to exclude them from regular activities most of us take for granted.
Not all disabilities are so visible. I have my own issues to deal with that keep me from living life *normally* and keeps me from participating in regular activities that most people take for granted. It ain't easy but that's life. I just avoid those situations and move on.