Complex sentence: The slogan is intended as a protest against the Autism Society of America's claim to be the voice of autism, and that their use of "the real voice of autism" refers to all autistic people, including those who disagree with Autistics.Org.
Split into simpler sentences: The slogan is intended as a protest against the Autism Society of America's claim to be the voice of autism. Autistics.Org says that their slogan "the real voice of autism" refers to all autistic people, including those who disagree with Autistics.Org.